[release] sudk v0.1.1

- added clippy lints and fixed the resulting issues
- moved build_possible_values_db() into the new() call
- extracted the skip_db functionality into their own functions

.gitignore

@@ -1 +1,2 @@
 /target
+/c_version/sudk_c

Cargo.lock

@@ -4,4 +4,4 @@ version = 3
 
 [[package]]
 name = "sudk"
-version = "0.1.0"
+version = "0.1.1"

Cargo.toml

@@ -1,13 +1,19 @@
 [package]
 name = "sudk"
-version = "0.1.0"
+version = "0.1.1"
 authors = ["ddidderr <ddidderr@paul.network>"]
 edition = "2021"
 
+[lints.clippy]
+pedantic = { level = "warn", priority = -1 }
+todo = "warn"
+unwrap_used = "warn"
+
 [dependencies]
 
 [profile.release]
 lto = true
 debug = false
-codegen-units = 1
+strip = true
 panic = "abort"
+codegen-units = 1

c_version/clangtest

@@ -0,0 +1,6 @@
+#!/bin/bash
+set -e
+
+clang -Weverything -Wno-unsafe-buffer-usage -Werror -O3 -march=native -flto -std=c17 -fstack-protector-all -s -o sudk_c "$1"
+
+time ./sudk_c

c_version/gcctest

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+set -e
+
+gcc -Wall -Wextra -Werror --std=c17 -march=native -O3 -fstack-protector-all -flto -s -o sudk_c "$1"
+
+time ./sudk_c

c_version/sudk_lots_of_allocs_for_tmp_rows_cols_blocks.c

@@ -0,0 +1,287 @@
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+
+#define PFSALLOC(bytes) malloc(bytes)
+
+static inline void Print_Clear() { printf("\x1b\x5b\x48\x1b\x5b\x32\x4a"); }
+
+typedef struct Sudoku {
+  size_t *field;
+  size_t *fixed;
+  size_t *known;
+  size_t size;
+  size_t block_size;
+  size_t pos;
+  size_t pos_last_placed;
+  size_t num_fields;
+} Sudoku;
+
+static Sudoku *Sudoku_New(size_t block_size) {
+
+  Sudoku *s = calloc(1, sizeof(Sudoku));
+
+  size_t many_solutions_field[81] = {
+      0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 8, 9, 0, 2, 0, 0, 0, 0,
+      0, 2, 0, 4, 0, 0, 0, 0, 4, 0, 6, 0, 0, 0, 8, 0, 0, 0, 5, 0, 0,
+      0, 0, 0, 0, 6, 5, 0, 0, 2, 0, 7, 4, 0, 3, 0, 0, 0, 5, 0, 4, 0,
+      0, 0, 1, 8, 0, 0, 0, 0, 0, 0, 0, 8, 2, 0, 0, 0, 6, 0,
+  };
+
+  size_t size = block_size * block_size;
+  size_t *field = calloc(size * size, sizeof(size_t));
+  size_t *fixed = calloc(size * size, sizeof(size_t));
+  size_t *known = calloc(size * size, sizeof(size_t));
+
+  printf("num_fields: %zu\n", size * size);
+
+  s->field = field;
+  s->fixed = fixed;
+  s->known = known;
+
+  for (size_t idx = 0; idx < 81; idx++) {
+    s->field[idx] = many_solutions_field[idx];
+  }
+
+  for (size_t idx = 0; idx < 81; idx++) {
+    if (s->field[idx] != 0) {
+      s->fixed[idx] = 1;
+      s->known[idx] = 1;
+    }
+  }
+
+  s->size = size;
+  s->block_size = block_size;
+  s->pos = 0;
+  s->pos_last_placed = 0;
+  s->num_fields = size * size;
+
+  return s;
+}
+
+static void Sudoku_Print(Sudoku *s) {
+  for (size_t idx = 0; idx < s->size * s->size; idx++) {
+
+    // newline
+    if (idx != 0 && idx % s->size == 0)
+      printf("\n");
+
+    // nr
+    printf("%zu", s->field[idx]);
+
+    // space
+    if ((idx + 1) % s->size != 0)
+      printf(" ");
+  }
+  printf("\n");
+}
+
+static inline bool Sudoku_Next(Sudoku *s) {
+  if (s->pos == s->num_fields - 1) {
+    /*printf("there is no next\n");*/
+    return false;
+  }
+
+  s->pos++;
+  return true;
+}
+
+static inline bool Sudoku_Prev(Sudoku *s) {
+  if (s->pos == 0)
+    return false;
+
+  s->pos--;
+  return true;
+}
+
+static inline bool Sudoku_IsFixed(Sudoku *s) { return s->fixed[s->pos] == 1; }
+
+static inline size_t Sudoku_GetFieldAtPos(Sudoku *s, size_t pos) {
+  return s->field[pos];
+}
+
+static inline void Sudoku_Set(Sudoku *s, size_t nr) {
+  s->field[s->pos] = nr;
+  s->pos_last_placed = s->pos;
+}
+
+static inline void Sudoku_ClearCurrentField(Sudoku *s) { Sudoku_Set(s, 0); }
+
+/*static void Array_Print(char *name, size_t *arr, size_t len) {*/
+/*printf("%s: ", name);*/
+/*for (size_t idx = 0; idx < len; idx++) {*/
+/*if (idx < len - 1)*/
+/*printf("%zu ", arr[idx]);*/
+/*else*/
+/*printf("%zu", arr[idx]);*/
+/*}*/
+/*printf("\n");*/
+/*}*/
+
+static inline bool Array_Contains(size_t *arr, size_t len, size_t nr) {
+  /*printf("ARRAY_CONTAINS_LEN: %zu\n", len);*/
+  for (size_t idx = 0; idx < len; idx++) {
+    if (arr[idx] == nr) {
+      /*printf("SEARCH FOR %zu --- ", nr);*/
+      /*Array_Print("ARRAY_CONTAINS_TRUE", arr, len);*/
+      return true;
+    }
+  }
+  /*printf("SEARCH FOR %zu --- ", nr);*/
+  /*Array_Print("ARRAY_CONTAINS_FALSE", arr, len);*/
+  return false;
+}
+
+static inline bool Sudoku_IsEnd(Sudoku *s) {
+  return !Array_Contains(s->field, s->num_fields, 0);
+}
+
+static inline bool Sudoku_GotoPrevFreeField(Sudoku *s) {
+  do {
+    if (!Sudoku_IsFixed(s))
+      return true;
+  } while (Sudoku_Prev(s));
+
+  return false;
+}
+
+static inline bool Sudoku_GotoNextFreeField(Sudoku *s) {
+  /*printf("Sudoku_GotoNextFreeField\n");*/
+  do {
+    if (!Sudoku_IsFixed(s))
+      return true;
+  } while (Sudoku_Next(s));
+
+  return false;
+}
+
+static inline size_t *Sudoku_GetRow(Sudoku *s) {
+  size_t *tmp = PFSALLOC(s->size * sizeof(size_t));
+  for (size_t pos = 0; pos < s->size; pos++) {
+    tmp[pos] = Sudoku_GetFieldAtPos(s, (s->pos / s->size) * s->size + pos);
+  }
+  return tmp;
+}
+
+static inline size_t *Sudoku_GetCol(Sudoku *s) {
+  size_t *tmp = PFSALLOC(s->size * sizeof(size_t));
+  for (size_t pos = 0; pos < s->size; pos++) {
+    tmp[pos] = Sudoku_GetFieldAtPos(s, pos * s->size + s->pos % s->size);
+  }
+  return tmp;
+}
+
+static inline size_t *Sudoku_GetBlock(Sudoku *s) {
+  size_t *tmp = PFSALLOC(s->size * sizeof(size_t));
+
+  size_t block_start_row = s->pos / s->size / s->block_size * s->block_size;
+  size_t block_start_col = s->pos % s->size / s->block_size * s->block_size;
+
+  for (size_t r = 0; r < s->block_size; r++) {
+    for (size_t c = 0; c < s->block_size; c++) {
+      tmp[r * s->block_size + c] = Sudoku_GetFieldAtPos(
+          s, s->size * (block_start_row + r) + block_start_col + c);
+    }
+  }
+  return tmp;
+}
+
+static inline bool Sudoku_BlockOk(Sudoku *s, size_t nr) {
+  size_t *block = Sudoku_GetBlock(s);
+  /*Array_Print("BLOCK", block, s->size);*/
+  bool ok = !Array_Contains(block, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_RowOk(Sudoku *s, size_t nr) {
+  size_t *row = Sudoku_GetRow(s);
+  bool ok = !Array_Contains(row, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_ColOk(Sudoku *s, size_t nr) {
+  size_t *col = Sudoku_GetCol(s);
+  bool ok = !Array_Contains(col, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_Ok(Sudoku *s, size_t nr) {
+  return Sudoku_BlockOk(s, nr) && Sudoku_ColOk(s, nr) && Sudoku_RowOk(s, nr);
+}
+
+static inline bool Sudoku_PutValidNr(Sudoku *s) {
+  size_t current_nr = Sudoku_GetFieldAtPos(s, s->pos);
+
+  /*printf("%s() pos=%zu current_nr=%zu\n", __func__, s->pos, current_nr);*/
+
+  for (size_t nr = current_nr; nr < s->size + 1; nr++) {
+    if (Sudoku_Ok(s, nr)) {
+      /*printf("%s() pos=%zu current_nr=%zu nr=%zu\n", __func__, s->pos,*/
+      /*current_nr, nr);*/
+      Sudoku_Set(s, nr);
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool Sudoku_SolveBacktracking(Sudoku *s) {
+  bool found_solution = false;
+  size_t num_solutions = 0;
+  while (1) {
+    /*printf("LOOP: pos=%zu\n", s->pos);*/
+    /*Sudoku_Print(s);*/
+    if (Sudoku_IsEnd(s)) {
+      /*printf("END\n");*/
+      found_solution = true;
+      num_solutions++;
+      if (num_solutions % 100 == 0) {
+        Print_Clear();
+        printf("Solutions: %zu\n", num_solutions);
+        Sudoku_Print(s);
+      }
+
+      if (Sudoku_IsFixed(s)) {
+        /*printf("fixed\n");*/
+        continue;
+      }
+      Sudoku_ClearCurrentField(s);
+      Sudoku_Prev(s);
+      Sudoku_GotoPrevFreeField(s);
+    }
+
+    if (Sudoku_IsFixed(s)) {
+      /*printf("fixed -> goto next\n");*/
+      Sudoku_Next(s);
+      continue;
+    }
+
+    if (Sudoku_GotoNextFreeField(s)) {
+      if (Sudoku_PutValidNr(s)) {
+        Sudoku_Next(s);
+        continue;
+      } else {
+        Sudoku_ClearCurrentField(s);
+        if (!Sudoku_Prev(s)) {
+          printf("Number of solutions: %zu\n", num_solutions);
+          break;
+        }
+        if (!Sudoku_GotoPrevFreeField(s)) {
+          printf("Number of solutions: %zu\n", num_solutions);
+          break;
+        }
+      }
+    }
+  }
+
+  return found_solution;
+}
+
+int main() {
+  Sudoku *s = Sudoku_New(3);
+  Sudoku_Print(s);
+  Sudoku_SolveBacktracking(s);
+  /*Sudoku_Print(s);*/
+}

c_version/sudk_no_alloc_instead_use_global_mut_mem_once_initialized_on_start.c

@@ -0,0 +1,278 @@
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+
+static size_t *tmpArr;
+
+static inline void Print_Clear() { printf("\x1b\x5b\x48\x1b\x5b\x32\x4a"); }
+
+typedef struct Sudoku {
+  size_t *field;
+  size_t *fixed;
+  size_t size;
+  size_t block_size;
+  size_t pos;
+  size_t pos_last_placed;
+  size_t num_fields;
+} Sudoku;
+
+static Sudoku *Sudoku_New(size_t block_size) {
+
+  Sudoku *s = calloc(1, sizeof(Sudoku));
+
+  size_t many_solutions_field[81] = {
+      0, 0, 0, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 8, 9, 0, 2, 0, 0, 0, 0,
+      0, 2, 0, 4, 0, 0, 0, 0, 4, 0, 6, 0, 0, 0, 8, 0, 0, 0, 5, 0, 0,
+      0, 0, 0, 0, 6, 5, 0, 0, 2, 0, 7, 4, 0, 3, 0, 0, 0, 5, 0, 4, 0,
+      0, 0, 1, 8, 0, 0, 0, 0, 0, 0, 0, 8, 2, 0, 0, 0, 6, 0,
+  };
+
+  size_t size = block_size * block_size;
+  size_t *field = calloc(size * size, sizeof(size_t));
+  size_t *fixed = calloc(size * size, sizeof(size_t));
+
+  printf("num_fields: %zu\n", size * size);
+
+  s->field = field;
+  s->fixed = fixed;
+
+  for (size_t idx = 0; idx < 81; idx++) {
+    s->field[idx] = many_solutions_field[idx];
+  }
+
+  for (size_t idx = 0; idx < 81; idx++) {
+    if (s->field[idx] != 0) {
+      s->fixed[idx] = 1;
+    }
+  }
+
+  s->size = size;
+  s->block_size = block_size;
+  s->pos = 0;
+  s->pos_last_placed = 0;
+  s->num_fields = size * size;
+
+  tmpArr = calloc(s->size, sizeof(size_t));
+
+  return s;
+}
+
+static void Sudoku_Print(Sudoku *s) {
+  for (size_t idx = 0; idx < s->size * s->size; idx++) {
+
+    // newline
+    if (idx != 0 && idx % s->size == 0)
+      printf("\n");
+
+    // nr
+    printf("%zu", s->field[idx]);
+
+    // space
+    if ((idx + 1) % s->size != 0)
+      printf(" ");
+  }
+  printf("\n");
+}
+
+static inline bool Sudoku_Next(Sudoku *s) {
+  if (s->pos == s->num_fields - 1) {
+    /*printf("there is no next\n");*/
+    return false;
+  }
+
+  s->pos++;
+  return true;
+}
+
+static inline bool Sudoku_Prev(Sudoku *s) {
+  if (s->pos == 0)
+    return false;
+
+  s->pos--;
+  return true;
+}
+
+static inline bool Sudoku_IsFixed(Sudoku *s) { return s->fixed[s->pos] == 1; }
+
+static inline size_t Sudoku_GetFieldAtPos(Sudoku *s, size_t pos) {
+  return s->field[pos];
+}
+
+static inline void Sudoku_Set(Sudoku *s, size_t nr) {
+  s->field[s->pos] = nr;
+  s->pos_last_placed = s->pos;
+}
+
+static inline void Sudoku_ClearCurrentField(Sudoku *s) { Sudoku_Set(s, 0); }
+
+static inline bool Array_Contains(size_t *arr, size_t len, size_t nr) {
+  /*printf("ARRAY_CONTAINS_LEN: %zu\n", len);*/
+  for (size_t idx = 0; idx < len; idx++) {
+    if (arr[idx] == nr) {
+      /*printf("SEARCH FOR %zu --- ", nr);*/
+      /*Array_Print("ARRAY_CONTAINS_TRUE", arr, len);*/
+      return true;
+    }
+  }
+  /*printf("SEARCH FOR %zu --- ", nr);*/
+  /*Array_Print("ARRAY_CONTAINS_FALSE", arr, len);*/
+  return false;
+}
+
+static inline bool Sudoku_IsEnd(Sudoku *s) {
+  return !Array_Contains(s->field, s->num_fields, 0);
+}
+
+static inline bool Sudoku_GotoPrevFreeField(Sudoku *s) {
+  do {
+    if (!Sudoku_IsFixed(s))
+      return true;
+  } while (Sudoku_Prev(s));
+
+  return false;
+}
+
+static inline bool Sudoku_GotoNextFreeField(Sudoku *s) {
+  /*printf("Sudoku_GotoNextFreeField\n");*/
+  do {
+    if (!Sudoku_IsFixed(s))
+      return true;
+  } while (Sudoku_Next(s));
+
+  return false;
+}
+
+static inline size_t *Sudoku_GetRow(Sudoku *s) {
+  for (size_t pos = 0; pos < s->size; pos++) {
+    tmpArr[pos] = Sudoku_GetFieldAtPos(s, (s->pos / s->size) * s->size + pos);
+  }
+  return tmpArr;
+}
+
+static inline size_t *Sudoku_GetCol(Sudoku *s) {
+  for (size_t pos = 0; pos < s->size; pos++) {
+    tmpArr[pos] = Sudoku_GetFieldAtPos(s, pos * s->size + s->pos % s->size);
+  }
+  return tmpArr;
+}
+
+static inline size_t *Sudoku_GetBlock(Sudoku *s) {
+  size_t block_start_row = s->pos / s->size / s->block_size * s->block_size;
+  size_t block_start_col = s->pos % s->size / s->block_size * s->block_size;
+
+  for (size_t r = 0; r < s->block_size; r++) {
+    for (size_t c = 0; c < s->block_size; c++) {
+      tmpArr[r * s->block_size + c] = Sudoku_GetFieldAtPos(
+          s, s->size * (block_start_row + r) + block_start_col + c);
+    }
+  }
+  return tmpArr;
+}
+
+static inline bool Sudoku_BlockOk(Sudoku *s, size_t nr) {
+  size_t *block = Sudoku_GetBlock(s);
+  /*Array_Print("BLOCK", block, s->size);*/
+  bool ok = !Array_Contains(block, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_RowOk(Sudoku *s, size_t nr) {
+  size_t *row = Sudoku_GetRow(s);
+  bool ok = !Array_Contains(row, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_ColOk(Sudoku *s, size_t nr) {
+  size_t *col = Sudoku_GetCol(s);
+  bool ok = !Array_Contains(col, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_Ok(Sudoku *s, size_t nr) {
+  return Sudoku_BlockOk(s, nr) && Sudoku_ColOk(s, nr) && Sudoku_RowOk(s, nr);
+}
+
+static inline bool Sudoku_PutValidNr(Sudoku *s) {
+  size_t current_nr = Sudoku_GetFieldAtPos(s, s->pos);
+
+  /*printf("%s() pos=%zu current_nr=%zu\n", __func__, s->pos, current_nr);*/
+
+  for (size_t nr = current_nr; nr < s->size + 1; nr++) {
+    if (Sudoku_Ok(s, nr)) {
+      /*printf("%s() pos=%zu current_nr=%zu nr=%zu\n", __func__, s->pos,*/
+      /*current_nr, nr);*/
+      Sudoku_Set(s, nr);
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool Sudoku_SolveBacktracking(Sudoku *s) {
+  bool found_solution = false;
+  size_t num_solutions = 0;
+  while (1) {
+    /*printf("LOOP: pos=%zu\n", s->pos);*/
+    /*Sudoku_Print(s);*/
+    if (Sudoku_IsEnd(s)) {
+      /*printf("END\n");*/
+      found_solution = true;
+      num_solutions++;
+      if (num_solutions % 100 == 0) {
+        Print_Clear();
+        printf("Solutions: %zu\n", num_solutions);
+        Sudoku_Print(s);
+      }
+
+      if (Sudoku_IsFixed(s)) {
+        /*printf("fixed\n");*/
+        continue;
+      }
+      Sudoku_ClearCurrentField(s);
+      Sudoku_Prev(s);
+      Sudoku_GotoPrevFreeField(s);
+    }
+
+    if (Sudoku_IsFixed(s)) {
+      /*printf("fixed -> goto next\n");*/
+      Sudoku_Next(s);
+      continue;
+    }
+
+    if (Sudoku_GotoNextFreeField(s)) {
+      if (Sudoku_PutValidNr(s)) {
+        Sudoku_Next(s);
+        continue;
+      } else {
+        Sudoku_ClearCurrentField(s);
+        if (!Sudoku_Prev(s)) {
+          printf("Number of solutions: %zu\n", num_solutions);
+          break;
+        }
+        if (!Sudoku_GotoPrevFreeField(s)) {
+          printf("Number of solutions: %zu\n", num_solutions);
+          break;
+        }
+      }
+    }
+  }
+
+  return found_solution;
+}
+
+static void Sudoku_Free(Sudoku *s) {
+  free(s->field);
+  free(s->fixed);
+  free(s);
+  s = NULL;
+}
+
+int main() {
+  Sudoku *s = Sudoku_New(3);
+  Sudoku_Print(s);
+  Sudoku_SolveBacktracking(s);
+  Sudoku_Free(s);
+  free(tmpArr);
+}

c_version/sudk_stack.c

@@ -0,0 +1,266 @@
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+
+static inline void Print_Clear(void) { printf("\x1b\x5b\x48\x1b\x5b\x32\x4a"); }
+
+typedef struct Sudoku {
+  uint8_t *field;
+  bool *fixed;
+  size_t size;
+  size_t block_size;
+  size_t pos;
+  size_t pos_last_placed;
+  size_t num_fields;
+} Sudoku;
+
+static Sudoku *Sudoku_New(size_t block_size) {
+
+  Sudoku *s = calloc(1, sizeof(Sudoku));
+
+  // clang-format off
+  uint8_t many_solutions_field[81] = {
+      0, 0, 0, 0, 0, 0, 0, 0, 9,
+      0, 0, 0, 0, 8, 9, 0, 2, 0,
+      0, 0, 0, 0, 2, 0, 4, 0, 0,
+      0, 0, 4, 0, 6, 0, 0, 0, 8,
+      0, 0, 0, 5, 0, 0, 0, 0, 0,
+      0, 6, 5, 0, 0, 2, 0, 7, 4,
+      0, 3, 0, 0, 0, 5, 0, 4, 0,
+      0, 0, 1, 8, 0, 0, 0, 0, 0,
+      0, 0, 8, 2, 0, 0, 0, 6, 0,
+  };
+  // clang-format on
+
+  size_t size = block_size * block_size;
+  uint8_t *field = calloc(size * size, sizeof(uint8_t));
+  bool *fixed = calloc(size * size, sizeof(bool));
+
+  printf("num_fields: %zu\n", size * size);
+
+  s->field = field;
+  s->fixed = fixed;
+
+  for (size_t idx = 0; idx < 81; idx++) {
+    s->field[idx] = many_solutions_field[idx];
+  }
+
+  for (size_t idx = 0; idx < 81; idx++) {
+    if (s->field[idx] != 0) {
+      s->fixed[idx] = true;
+    }
+  }
+
+  s->size = size;
+  s->block_size = block_size;
+  s->pos = 0;
+  s->pos_last_placed = 0;
+  s->num_fields = size * size;
+
+  return s;
+}
+
+static inline void Sudoku_Print(Sudoku *s) {
+  for (size_t idx = 0; idx < s->num_fields; idx++) {
+
+    // newline
+    if (idx != 0 && idx % s->size == 0)
+      printf("\n");
+
+    // nr
+    printf("%hhu", s->field[idx]);
+
+    // space
+    if ((idx + 1) % s->size != 0)
+      printf(" ");
+  }
+  printf("\n");
+}
+
+static inline bool Sudoku_Next(Sudoku *s) {
+  if (s->pos == s->num_fields - 1) {
+    return false;
+  }
+
+  s->pos++;
+  return true;
+}
+
+static inline bool Sudoku_Prev(Sudoku *s) {
+  if (s->pos == 0)
+    return false;
+
+  s->pos--;
+  return true;
+}
+
+static inline bool Sudoku_IsFixed(Sudoku *s) { return s->fixed[s->pos]; }
+
+static inline uint8_t Sudoku_GetFieldAtPos(Sudoku *s, size_t pos) {
+  return s->field[pos];
+}
+
+static inline void Sudoku_Set(Sudoku *s, uint8_t nr) {
+  s->field[s->pos] = nr;
+  s->pos_last_placed = s->pos;
+}
+
+static inline void Sudoku_ClearCurrentField(Sudoku *s) { Sudoku_Set(s, 0); }
+
+static inline bool Array_Contains(uint8_t *arr, size_t len, uint8_t nr) {
+  for (size_t idx = 0; idx < len; idx++) {
+    if (arr[idx] == nr) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static inline bool Sudoku_IsEnd(Sudoku *s) {
+  return !Array_Contains(s->field, s->num_fields, 0);
+}
+
+static inline bool Sudoku_GotoPrevFreeField(Sudoku *s) {
+  do {
+    if (!Sudoku_IsFixed(s))
+      return true;
+  } while (Sudoku_Prev(s));
+
+  return false;
+}
+
+static inline bool Sudoku_GotoNextFreeField(Sudoku *s) {
+  do {
+    if (!Sudoku_IsFixed(s))
+      return true;
+  } while (Sudoku_Next(s));
+
+  return false;
+}
+
+static inline void Sudoku_GetRow(Sudoku *s, uint8_t *row) {
+  for (size_t pos = 0; pos < s->size; pos++) {
+    row[pos] = Sudoku_GetFieldAtPos(s, (s->pos / s->size) * s->size + pos);
+  }
+}
+
+static inline void Sudoku_GetCol(Sudoku *s, uint8_t *col) {
+  for (size_t pos = 0; pos < s->size; pos++) {
+    col[pos] = Sudoku_GetFieldAtPos(s, pos * s->size + s->pos % s->size);
+  }
+}
+
+static inline void Sudoku_GetBlock(Sudoku *s, uint8_t *block) {
+  size_t block_start_row = s->pos / s->size / s->block_size * s->block_size;
+  size_t block_start_col = s->pos % s->size / s->block_size * s->block_size;
+
+  for (size_t r = 0; r < s->block_size; r++) {
+    for (size_t c = 0; c < s->block_size; c++) {
+      block[r * s->block_size + c] = Sudoku_GetFieldAtPos(
+          s, s->size * (block_start_row + r) + block_start_col + c);
+    }
+  }
+}
+
+static inline bool Sudoku_BlockOk(Sudoku *s, uint8_t nr) {
+  bool ok;
+  uint8_t block[9] = {0};
+  Sudoku_GetBlock(s, block);
+  ok = !Array_Contains(block, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_RowOk(Sudoku *s, uint8_t nr) {
+  bool ok;
+  uint8_t row[9] = {0};
+  Sudoku_GetRow(s, row);
+  ok = !Array_Contains(row, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_ColOk(Sudoku *s, uint8_t nr) {
+  bool ok;
+  uint8_t col[9] = {0};
+  Sudoku_GetCol(s, col);
+  ok = !Array_Contains(col, s->size, nr);
+  return ok;
+}
+
+static inline bool Sudoku_Ok(Sudoku *s, uint8_t nr) {
+  return Sudoku_BlockOk(s, nr) && Sudoku_ColOk(s, nr) && Sudoku_RowOk(s, nr);
+}
+
+static inline bool Sudoku_PutValidNr(Sudoku *s) {
+  uint8_t current_nr = Sudoku_GetFieldAtPos(s, s->pos);
+  for (uint8_t nr = current_nr; nr < s->size + 1; nr++) {
+    if (Sudoku_Ok(s, nr)) {
+      Sudoku_Set(s, nr);
+      return true;
+    }
+  }
+  return false;
+}
+
+static bool Sudoku_SolveBacktracking(Sudoku *s) {
+  bool found_solution = false;
+  size_t num_solutions = 0;
+  while (1) {
+    if (Sudoku_IsEnd(s)) {
+      found_solution = true;
+      num_solutions++;
+      if (num_solutions % 100 == 0) {
+        Print_Clear();
+        printf("Solutions: %zu\n", num_solutions);
+        Sudoku_Print(s);
+      }
+
+      if (Sudoku_IsFixed(s)) {
+        continue;
+      }
+      Sudoku_ClearCurrentField(s);
+      Sudoku_Prev(s);
+      Sudoku_GotoPrevFreeField(s);
+    }
+
+    if (Sudoku_IsFixed(s)) {
+      Sudoku_Next(s);
+      continue;
+    }
+
+    if (Sudoku_GotoNextFreeField(s)) {
+      if (Sudoku_PutValidNr(s)) {
+        Sudoku_Next(s);
+        continue;
+      } else {
+        Sudoku_ClearCurrentField(s);
+        if (!Sudoku_Prev(s)) {
+          printf("Number of solutions: %zu\n", num_solutions);
+          break;
+        }
+        if (!Sudoku_GotoPrevFreeField(s)) {
+          printf("Number of solutions: %zu\n", num_solutions);
+          break;
+        }
+      }
+    }
+  }
+
+  return found_solution;
+}
+
+static void Sudoku_Free(Sudoku *s) {
+  free(s->field);
+  free(s->fixed);
+  free(s);
+  s = NULL;
+}
+
+int main(void) {
+  Sudoku *s = Sudoku_New(3);
+  Sudoku_Print(s);
+  Sudoku_SolveBacktracking(s);
+  Sudoku_Free(s);
+}

rustfmt.toml

@@ -0,0 +1,3 @@
+group_imports = "StdExternalCrate"
+imports_granularity = "Crate"
+imports_layout = "HorizontalVertical"

src/main.rs

@@ -1,52 +1,39 @@
 use std::time::Instant;
 
+const BLOCK_SIZE: usize = 3;
+const SIZE: usize = BLOCK_SIZE * BLOCK_SIZE;
+const NUM_FIELDS: usize = SIZE * SIZE;
+
+fn print_gray() {
+    print!("\x1b\x5b\x31\x3b\x33\x30\x6d");
+}
+
+fn print_green() {
+    print!("\x1b\x5b\x31\x3b\x33\x32\x6d");
+}
+
+fn print_neutral() {
+    print!("\x1b\x5b\x31\x3b\x30\x6d");
+}
+
+fn print_clear() {
+    print!("\x1b\x5b\x48\x1b\x5b\x32\x4a");
+}
+
 struct SField {
-    field: Vec<usize>,
-    rows: Vec<Vec<usize>>,
-    cols: Vec<Vec<usize>>,
-    blocks: Vec<Vec<usize>>,
-    fixed: Vec<usize>,
-    size: usize,
-    block_size: usize,
+    field: Vec<u8>,
+    skip_forward: Vec<u8>,
+    skip_backward: Vec<u8>,
     pos: usize,
-    pos_last_placed: usize,
-    num_fields: usize,
-    possible_values: Vec<Vec<usize>>,
+    possible_values: Vec<Vec<u8>>,
 }
 
 impl SField {
-    pub fn new(block_size: usize) -> SField {
-        let size = block_size * block_size;
-
-        // EMPTY FIELD
-        // let field = vec![0; size * size];
-
-        // BLOCK_SIZE 4
-        // #[rustfmt::skip]
-        // let field = vec![
-        //     0,15,0,0,0,0,11,4,0,5,0,0,0,0,12,8,
-        //     12,0,0,9,0,1,0,5,0,0,8,15,0,0,0,13,
-        //     0,0,3,0,0,10,13,0,0,11,4,0,15,0,6,0,
-        //     13,10,0,11,0,0,0,14,0,3,2,0,0,9,0,0,
-        //     0,0,15,10,8,0,0,0,0,0,14,0,0,6,2,0,
-        //     0,0,14,0,0,0,6,0,0,0,0,0,1,0,0,0,
-        //     0,11,0,8,3,0,15,1,6,0,0,0,0,0,0,7,
-        //     0,6,0,7,0,0,0,0,8,13,0,0,10,0,0,0,
-        //     0,14,0,2,0,0,0,0,3,0,5,0,11,15,9,0,
-        //     0,0,0,12,11,0,2,0,0,0,0,0,0,0,0,0,
-        //     0,8,0,0,6,14,1,0,13,15,0,0,0,0,0,10,
-        //     10,0,0,3,9,0,7,0,0,1,0,0,13,12,8,0,
-        //     7,0,0,0,0,0,14,0,0,0,0,0,0,0,0,9,
-        //     0,3,0,14,0,0,9,6,0,0,0,0,0,4,0,0,
-        //     0,4,6,0,0,7,0,0,0,0,0,0,0,0,0,0,
-        //     5,2,0,0,0,4,10,15,1,0,3,0,0,0,7,0,
-        // ];
-
-        // MANY SOLUTIONS
+    pub fn new() -> SField {
         #[rustfmt::skip]
         let field = vec![
-            0,0,0,0,0,0,0,0,9,
-            0,0,0,0,8,9,0,2,0,
+            0,0,0,0,0,0,0,0,0,
+            0,0,0,0,8,9,0,0,0,
             0,0,0,0,2,0,4,0,0,
             0,0,4,0,6,0,0,0,8,
             0,0,0,5,0,0,0,0,0,
@@ -56,116 +43,72 @@ impl SField {
             0,0,8,2,0,0,0,6,0,
         ];
 
-        // HARD
-        // #[rustfmt::skip]
-        // let field = vec![
-        //     8,4,0,0,6,0,5,0,1,
-        //     0,0,0,0,0,3,0,4,0,
-        //     0,0,6,9,0,0,0,0,7,
-        //     0,2,0,7,1,0,0,0,6,
-        //     0,0,0,6,3,0,0,0,0,
-        //     9,0,0,0,0,0,0,5,0,
-        //     0,0,0,0,4,0,0,6,0,
-        //     2,0,0,0,0,0,1,8,0,
-        //     0,0,5,0,0,0,3,0,0,
-        // ];
-
-        // EASY
-        // #[rustfmt::skip]
-        // let field = vec![
-        //     5,9,0,6,1,3,0,0,0,
-        //     0,0,0,9,0,0,5,0,0,
-        //     8,0,3,0,5,7,6,4,0,
-        //     0,7,5,0,0,0,4,0,6,
-        //     0,6,0,7,4,0,2,0,8,
-        //     2,0,8,0,0,0,7,5,3,
-        //     0,0,0,5,6,1,0,7,0,
-        //     0,0,1,0,7,0,9,0,0,
-        //     7,3,6,0,2,0,0,0,0,
-        // ];
-
-        let mut fixed = Vec::with_capacity(size * size);
-        field.iter().for_each(|e| {
-            if *e == 0 {
-                fixed.push(0);
-            } else {
-                fixed.push(1);
-            }
-        });
-
-        let rows = SField::rows_from_plain_field(&field);
-        let cols = SField::cols_from_plain_field(&field);
-        let blocks = SField::blocks_from_plain_field(&field);
-
-        SField {
+        let mut sudoku = SField {
             field,
-            rows,
-            cols,
-            blocks,
-            fixed,
-            size,
-            block_size,
+            skip_forward: vec![0; NUM_FIELDS + 1],
+            skip_backward: vec![0; NUM_FIELDS + 1],
             pos: 0,
-            pos_last_placed: 0,
-            num_fields: size * size,
-            possible_values: vec![vec![]; size * size],
+            possible_values: vec![vec![]; NUM_FIELDS],
+        };
+
+        sudoku.build_possible_values_db();
+
+        sudoku.build_skip_dbs();
+
+        sudoku
+    }
+
+    fn build_skip_dbs(&mut self) {
+        fn find_fixed_streak_forward(mut idx: usize, field: &[u8]) -> u8 {
+            let mut fixed_count = 1;
+            idx += 1;
+
+            while idx < NUM_FIELDS && field[idx] > 0 {
+                fixed_count += 1;
+                idx += 1;
+            }
+
+            fixed_count
+        }
+
+        fn find_fixed_streak_backward(mut idx: usize, field: &[u8]) -> u8 {
+            let mut fixed_count = 1;
+            idx -= 1;
+
+            while idx < NUM_FIELDS && field[idx] > 0 {
+                fixed_count += 1;
+                idx -= 1;
+            }
+
+            fixed_count
+        }
+
+        let fwd = &mut self.skip_forward;
+        for (idx, nr) in self.field.iter().enumerate() {
+            match nr {
+                0 => fwd[idx] = *nr,
+                _ => fwd[idx] = find_fixed_streak_forward(idx, &self.field),
             }
         }
 
-    fn rows_from_plain_field(field: &[usize]) -> Vec<Vec<usize>> {
-        let mut rows = vec![vec![0; 9]; 9];
-        for row in 0..9 {
-            for col in 0..9 {
-                rows[row][col] = field[row * 9 + col];
+        let bwd = &mut self.skip_backward;
+        for (idx, nr) in self.field.iter().enumerate().rev() {
+            match nr {
+                0 => bwd[idx + 1] = *nr,
+                _ => bwd[idx + 1] = find_fixed_streak_backward(idx, &self.field),
             }
         }
-        rows
-    }
-
-    fn cols_from_plain_field(field: &[usize]) -> Vec<Vec<usize>> {
-        let mut cols = vec![vec![0; 9]; 9];
-        for row in 0..9 {
-            for col in 0..9 {
-                cols[col][row] = field[row * 9 + col];
-            }
-        }
-        cols
-    }
-
-    fn blocks_from_plain_field(field: &[usize]) -> Vec<Vec<usize>> {
-        fn get_block_with_pos(field: &[usize], pos: usize) -> Vec<usize> {
-            let block_start_row = pos / 9 / 3 * 3;
-            let block_start_col = pos % 9 / 3 * 3;
-
-            let mut block = vec![];
-
-            for r in 0..3 {
-                for c in 0..3 {
-                    block.push(field[9 * (block_start_row + r) + block_start_col + c])
-                }
-            }
-
-            block
-        }
-
-        let mut blocks = vec![];
-        let block_start_positions = [0, 3, 6, 27, 30, 33, 54, 57, 60];
-        for pos in block_start_positions {
-            blocks.push(get_block_with_pos(field, pos));
-        }
-
-        blocks
     }
 
     fn build_possible_values_db(&mut self) {
-        for idx in 0..self.num_fields {
-            if self.fixed[idx] == 1 {
+        for idx in 0..NUM_FIELDS {
+            if self.field[idx] != 0 {
                 continue;
             }
             self.pos = idx;
             // try all values between 1 and =self.size and remember the good ones
-            let mut good_ones = Vec::with_capacity(self.size);
-            for nr in 1..=self.size {
+            let mut good_ones = Vec::with_capacity(SIZE);
+            for nr in 1..=(u8::try_from(SIZE).expect("SIZE is too big")) {
                 if self.ok(nr) {
                     good_ones.push(nr);
                 }
@@ -176,166 +119,70 @@ impl SField {
     }
 
     pub fn solve_backtracking(&mut self) -> bool {
-        let mut found_solution = false;
         let mut num_solutions = 0;
 
-        //let mut loop_count = 0;
         loop {
-            //std::thread::sleep_ms(30);
-            //self.print_clear();
-            //self.print();
-            //loop_count += 1;
-            //if loop_count % 1000000 == 0 {
-            //self.print_clear();
-            //self.print();
-            //}
-            if self.is_end() {
-                found_solution = true;
-                num_solutions += 1;
-                if num_solutions % 100 == 0 {
-                    self.print_clear();
-                    println!("Solutions: {}", num_solutions);
-                    self.print();
-                }
-
-                if self.is_fixed() {
-                    continue;
-                }
-                self.clear_current_field();
-                self.prev();
-                self.goto_prev_free_field();
-            }
-
-            if self.is_fixed() {
-                self.next();
-                continue;
-            }
-
-            if self.goto_next_free_field() {
-                if self.put_valid_nr() {
-                    self.next();
-                    continue;
-                } else {
-                    //println!("put_valid_nr failed for pos {}", self.pos);
-                    //std::thread::sleep_ms(300);
+            if !self.put_valid_nr() {
                 self.clear_current_field();
                 if !self.prev() {
-                        println!("Number of solutions: {}", num_solutions);
+                    print_clear();
+                    self.print();
+                    println!("Number of solutions: {num_solutions}");
                     break;
                 }
-                    if !self.goto_prev_free_field() {
-                        println!("Number of solutions: {}", num_solutions);
-                        break;
+                continue;
             }
+
+            if !self.next() {
+                num_solutions += 1;
+                if num_solutions % 10_000 == 0 {
+                    print_clear();
+                    self.print();
+                    println!("Number of solutions: {num_solutions}");
                 }
+
+                self.clear_current_field();
+                self.prev();
             }
         }
 
-        found_solution
+        num_solutions > 0
     }
 
-    #[inline(always)]
-    fn print_gray(&self) {
-        print!("\x1b\x5b\x31\x3b\x33\x30\x6d");
-    }
-
-    #[inline(always)]
-    fn print_green(&self) {
-        print!("\x1b\x5b\x31\x3b\x33\x32\x6d");
-    }
-
-    #[inline(always)]
-    fn print_red(&self) {
-        print!("\x1b\x5b\x31\x3b\x33\x31\x6d");
-    }
-
-    #[inline(always)]
-    fn print_neutral(&self) {
-        print!("\x1b\x5b\x31\x3b\x30\x6d");
-    }
-
-    #[inline(always)]
-    fn print_clear(&self) {
-        print!("\x1b\x5b\x48\x1b\x5b\x32\x4a");
-    }
-
-    #[inline(always)]
     fn print(&self) {
-        for i in 0..self.num_fields {
-            if i != 0 && i % self.size == 0 {
+        for i in 0..NUM_FIELDS {
+            if i != 0 && i % SIZE == 0 {
                 println!();
             }
 
-            if i == self.pos_last_placed {
-                self.print_red();
-            } else if i == self.pos {
-                self.print_green();
+            if i == self.pos {
+                print_green();
             } else if self.get_field_at_pos(i) == 0 {
-                self.print_gray();
+                print_gray();
             }
 
             print!("{:2} ", self.get_field_at_pos(i));
 
-            if i == self.pos || i == self.pos_last_placed || self.get_field_at_pos(i) == 0 {
-                self.print_neutral();
+            if i == self.pos || self.get_field_at_pos(i) == 0 {
+                print_neutral();
             }
         }
         println!();
     }
 
-    #[inline(always)]
     fn clear_current_field(&mut self) {
         self.set(0);
     }
 
-    #[inline(always)]
-    fn goto_prev_free_field(&mut self) -> bool {
-        while {
-            if !self.is_fixed() {
-                return true;
-            }
-            self.prev()
-        } {}
-
-        false
-    }
-
-    #[inline(always)]
-    fn goto_next_free_field(&mut self) -> bool {
-        while {
-            if !self.is_fixed() {
-                return true;
-            }
-            self.next()
-        } {}
-
-        false
-    }
-
-    #[inline(always)]
-    fn _put_valid_nr(&mut self) -> bool {
-        let current_nr = self.get_field_at_pos(self.pos);
-
-        for nr in current_nr..self.size + 1 {
-            if self.ok(nr) {
-                self.set(nr);
-                return true;
-            }
-        }
-
-        false
-    }
-
-    #[inline(always)]
     fn put_valid_nr(&mut self) -> bool {
         let current_nr = self.get_field_at_pos(self.pos);
 
         // safety:
         //     self.possible_vals is initialized with self.size * self.size
         //     so self.pos can safely be used to index here
-        let possible_vals = unsafe { self.possible_values.get_unchecked(self.pos) };
+        let possible_vals = &self.possible_values[self.pos];
 
-        for nr in possible_vals.iter() {
+        for nr in possible_vals {
             if *nr <= current_nr {
                 continue;
             }
@@ -348,33 +195,11 @@ impl SField {
         false
     }
 
-    #[inline(always)]
-    fn is_end(&self) -> bool {
-        !self.field.contains(&0)
-    }
-
-    #[inline(always)]
-    fn ok(&self, nr: usize) -> bool {
+    fn ok(&self, nr: u8) -> bool {
         self.block_ok(nr) && self.row_ok(nr) && self.col_ok(nr)
     }
 
-    #[inline(always)]
-    fn _pos_to_xy(&self) -> (usize, usize) {
-        let y = self.pos / self.size;
-        let x = self.pos % self.size;
-        (x + 1, y + 1)
-    }
-
-    #[inline(always)]
-    fn is_fixed(&self) -> bool {
-        // safety: self.pos can be used to index the field unchecked
-        //         since the only methods modifying self.pos are
-        //         `next()` and `prev()` and they do bounds checking
-        unsafe { *self.fixed.get_unchecked(self.pos) == 1 }
-    }
-
-    #[inline(always)]
-    fn get_field_at_pos(&self, pos: usize) -> usize {
+    fn get_field_at_pos(&self, pos: usize) -> u8 {
         // safety:
         //     TODO
         //     would need to mathematically explain that the calculations in
@@ -382,187 +207,84 @@ impl SField {
         unsafe { *self.field.get_unchecked(pos) }
     }
 
-    #[inline(always)]
-    fn get_x_y_block_blockoffset(&self) -> (usize, usize, usize, usize) {
-        // TODO:
-        // this only works for 3x3 sudoku
-        #[rustfmt::skip]
-        let block_nrs = [
-             0, 1, 2, 9,10,11,18,19,20,
-             3, 4, 5,12,13,14,21,22,23,
-             6, 7, 8,15,16,17,24,25,26,
-            27,28,29,36,37,38,45,46,47,
-            30,31,32,39,40,41,48,49,50,
-            33,34,35,42,43,44,51,52,53,
-            54,55,56,63,64,65,72,73,74,
-            57,58,59,66,67,68,75,76,77,
-            60,61,62,69,70,71,78,79,80,
-        ];
-
-        let y = self.pos / self.size;
-        let x = self.pos % self.size;
-
-        let block_field = unsafe { block_nrs.get_unchecked(self.pos) };
-
-        let block_nr = block_field / self.size;
-        let block_offset = block_field - (block_nr * self.size);
-
-        (x, y, block_nr, block_offset)
-    }
-
-    #[inline(always)]
-    fn set(&mut self, nr: usize) {
-        //assert_eq!(self.field, self.flatten_rows());
-        //assert_eq!(self.field, self.flatten_cols());
-        //assert_eq!(self.field, self.flatten_blocks());
-
+    fn set(&mut self, nr: u8) {
         self.field[self.pos] = nr;
-        self.pos_last_placed = self.pos;
-
-        // update rows, cols and blocks
-        // this is more expensive than only updating field but should be outweight
-        // by the fact that row_ok(), col_ok() and block_ok() just need to do simple
-        // lookups now
-
-        let (x, y, block_nr, block_offset) = self.get_x_y_block_blockoffset();
-
-        //println!("[{},{}] setting {}", y, x, nr);
-
-        let row = unsafe { self.rows.get_unchecked_mut(y) };
-        let value = unsafe { row.get_unchecked_mut(x) };
-        *value = nr;
-
-        let col = unsafe { self.cols.get_unchecked_mut(x) };
-        let value = unsafe { col.get_unchecked_mut(y) };
-        *value = nr;
-
-        let block = unsafe { self.blocks.get_unchecked_mut(block_nr) };
-        let value = unsafe { block.get_unchecked_mut(block_offset) };
-        *value = nr;
-
-        //assert_eq!(self.field, self.flatten_rows());
-        //assert_eq!(self.field, self.flatten_cols());
-        //assert_eq!(self.field, self.flatten_blocks());
     }
 
-    #[inline(always)]
-    fn block_ok(&self, nr: usize) -> bool {
-        // TODO
-        // works only on 3x3 sudoku
-        #[rustfmt::skip]
-        let block_nrs = [
-            0,0,0,1,1,1,2,2,2,
-            0,0,0,1,1,1,2,2,2,
-            0,0,0,1,1,1,2,2,2,
-            3,3,3,4,4,4,5,5,5,
-            3,3,3,4,4,4,5,5,5,
-            3,3,3,4,4,4,5,5,5,
-            6,6,6,7,7,7,8,8,8,
-            6,6,6,7,7,7,8,8,8,
-            6,6,6,7,7,7,8,8,8,
-        ];
-
-        let block_nr = unsafe { block_nrs.get_unchecked(self.pos) };
-        //println!("Block {}: {:?}", block_nr, self.blocks[*block_nr]);
-        !unsafe { self.blocks.get_unchecked(*block_nr) }.contains(&nr)
+    fn get_row(&self, row: &mut [u8; SIZE]) {
+        for (idx, row_elem) in row.iter_mut().enumerate() {
+            *row_elem = self.get_field_at_pos((self.pos / SIZE) * SIZE + idx);
+        }
     }
 
-    #[inline(always)]
-    fn row_ok(&self, nr: usize) -> bool {
-        let row_nr = self.pos / self.size;
-        //println!("{:?}", self.rows[row_nr]);
-        !unsafe { self.rows.get_unchecked(row_nr) }.contains(&nr)
+    fn get_col(&self, col: &mut [u8; SIZE]) {
+        for (idx, col_elem) in col.iter_mut().enumerate() {
+            *col_elem = self.get_field_at_pos(idx * SIZE + self.pos % SIZE);
+        }
     }
 
-    #[inline(always)]
-    fn col_ok(&self, nr: usize) -> bool {
-        let col_nr = self.pos % self.size;
-        //println!("{:?}", self.cols[col_nr]);
-        !unsafe { self.cols.get_unchecked(col_nr) }.contains(&nr)
+    fn get_block(&self, block: &mut [u8; SIZE]) {
+        let block_start_row = self.pos / SIZE / BLOCK_SIZE * BLOCK_SIZE;
+        let block_start_col = self.pos % SIZE / BLOCK_SIZE * BLOCK_SIZE;
+
+        for r in 0..BLOCK_SIZE {
+            for c in 0..BLOCK_SIZE {
+                block[r * BLOCK_SIZE + c] =
+                    self.get_field_at_pos(SIZE * (block_start_row + r) + block_start_col + c);
+            }
+        }
+    }
+
+    fn block_ok(&self, nr: u8) -> bool {
+        let mut block = [0; SIZE];
+        self.get_block(&mut block);
+        !block.contains(&nr)
+    }
+
+    fn row_ok(&self, nr: u8) -> bool {
+        let mut row = [0; SIZE];
+        self.get_row(&mut row);
+        !row.contains(&nr)
+    }
+
+    fn col_ok(&self, nr: u8) -> bool {
+        let mut col = [0; SIZE];
+        self.get_col(&mut col);
+        !col.contains(&nr)
     }
 
-    #[inline(always)]
     fn next(&mut self) -> bool {
-        if self.pos == self.num_fields - 1 {
+        let new_pos = self.pos + 1 + self.skip_forward[self.pos + 1] as usize;
+
+        if new_pos >= NUM_FIELDS {
             return false;
         }
 
-        self.pos += 1;
+        self.pos = new_pos;
         true
     }
 
-    #[inline(always)]
     fn prev(&mut self) -> bool {
-        if self.pos == 0 {
+        let new_pos = self.pos - 1 - self.skip_backward[self.pos] as usize;
+
+        if new_pos >= NUM_FIELDS {
             return false;
         }
 
-        self.pos -= 1;
+        self.pos = new_pos;
         true
     }
 
-    #[inline(always)]
     fn solve(&mut self) {
         let now = Instant::now();
         if !self.solve_backtracking() {
             println!("there is no solution.");
         }
-        println!("took {:.3} seconds", now.elapsed().as_secs_f64());
+        eprintln!("took {:.3}s", now.elapsed().as_secs_f64());
     }
-
-    //fn flatten_blocks(&self) -> Vec<usize> {
-    //#[rustfmt::skip]
-    //let block_nrs = [
-    //0, 1, 2, 9,10,11,18,19,20,
-    //3, 4, 5,12,13,14,21,22,23,
-    //6, 7, 8,15,16,17,24,25,26,
-    //27,28,29,36,37,38,45,46,47,
-    //30,31,32,39,40,41,48,49,50,
-    //33,34,35,42,43,44,51,52,53,
-    //54,55,56,63,64,65,72,73,74,
-    //57,58,59,66,67,68,75,76,77,
-    //60,61,62,69,70,71,78,79,80,
-    //];
-
-    //let mut flattened = Vec::with_capacity(self.num_fields);
-    //for (idx, nr) in block_nrs.iter().enumerate() {
-    //let block_nr = nr / self.size;
-    //let block_offset = nr - (block_nr * self.size);
-    //flattened.push(self.blocks[block_nr][block_offset]);
-    //}
-    //flattened
-    //}
-
-    //fn flatten_rows(&self) -> Vec<usize> {
-    //let mut flattened = Vec::with_capacity(self.num_fields);
-    //for row in self.rows.iter() {
-    //for val in row {
-    //flattened.push(*val);
-    //}
-    //}
-    //flattened
-    //}
-
-    //fn flatten_cols(&self) -> Vec<usize> {
-    //let mut flattened = Vec::with_capacity(self.num_fields);
-    //for idx in 0..self.num_fields {
-    //flattened.push(self.cols[idx % self.size][idx / self.size]);
-    //}
-    //flattened
-    //}
-}
-
-fn run() -> Result<(), String> {
-    let mut field = SField::new(3);
-
-    field.build_possible_values_db();
-
-    field.solve();
-    Ok(())
 }
 
 fn main() {
-    if let Err(e) = run() {
-        println!("{}", e)
-    }
+    let mut field = SField::new();
+    field.solve();
 }