rust version: old method comparable to method in main

.cargo/config.toml

@@ -0,0 +1,2 @@
+[build]
+rustflags = ["-C", "target-cpu=native", "-C", "target-feature=+crt-static"]

.gitignore

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

Cargo.toml

@@ -9,5 +9,6 @@ edition = "2021"
 [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 -Wall -Wextra -Weverything -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() { 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() {
+  Sudoku *s = Sudoku_New(3);
+  Sudoku_Print(s);
+  Sudoku_SolveBacktracking(s);
+  Sudoku_Free(s);
+}

src/main.rs

@@ -1,47 +1,22 @@
+use std::time::Instant;
+
+const BLOCK_SIZE: usize = 3;
+const SIZE: usize = BLOCK_SIZE * BLOCK_SIZE;
+const NUM_FIELDS: usize = SIZE * SIZE;
+
 struct SField {
-    field: Vec<usize>,
-    fixed: Vec<usize>,
-    size: usize,
-    block_size: usize,
+    field: Vec<u8>,
+    fixed: Vec<bool>,
     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,
@@ -51,64 +26,32 @@ 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);
+        let mut fixed = Vec::with_capacity(SIZE * SIZE);
         field.iter().for_each(|e| {
             if *e == 0 {
-                fixed.push(0);
+                fixed.push(false);
             } else {
-                fixed.push(1);
+                fixed.push(true);
             }
         });
 
         SField {
             field,
             fixed,
-            size,
-            block_size,
             pos: 0,
-            pos_last_placed: 0,
-            num_fields: size * size,
-            possible_values: vec![vec![]; size * size],
+            possible_values: vec![vec![]; SIZE * SIZE],
         }
     }
 
     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.fixed[idx] {
                 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..=(SIZE as u8) {
                 if self.ok(nr) {
                     good_ones.push(nr);
                 }
@@ -119,26 +62,15 @@ 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 {
+
+                if num_solutions % 10_000 == 0 {
                     self.print_clear();
-                    println!("Solutions: {}", num_solutions);
                     self.print();
+                    println!("Number of solutions: {}", num_solutions);
                 }
 
                 if self.is_fixed() {
@@ -159,8 +91,6 @@ impl SField {
                     self.next();
                     continue;
                 } else {
-                    //println!("put_valid_nr failed for pos {}", self.pos);
-                    //std::thread::sleep_ms(300);
                     self.clear_current_field();
                     if !self.prev() {
                         println!("Number of solutions: {}", num_solutions);
@@ -174,7 +104,7 @@ impl SField {
             }
         }
 
-        found_solution
+        num_solutions > 0
     }
 
     #[inline(always)]
@@ -187,11 +117,6 @@ impl SField {
         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");
@@ -204,14 +129,12 @@ impl SField {
 
     #[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 {
+            if i == self.pos {
                 self.print_green();
             } else if self.get_field_at_pos(i) == 0 {
                 self.print_gray();
@@ -219,7 +142,7 @@ impl SField {
 
             print!("{:2} ", self.get_field_at_pos(i));
 
-            if i == self.pos || i == self.pos_last_placed || self.get_field_at_pos(i) == 0 {
+            if i == self.pos || self.get_field_at_pos(i) == 0 {
                 self.print_neutral();
             }
         }
@@ -259,7 +182,7 @@ impl SField {
     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 {
+        for nr in current_nr..(SIZE + 1) as u8 {
             if self.ok(nr) {
                 self.set(nr);
                 return true;
@@ -297,14 +220,14 @@ impl SField {
     }
 
     #[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;
+        let y = self.pos / SIZE;
+        let x = self.pos % SIZE;
         (x + 1, y + 1)
     }
 
@@ -313,11 +236,11 @@ impl SField {
         // 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 }
+        unsafe { *self.fixed.get_unchecked(self.pos) }
     }
 
     #[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
@@ -326,62 +249,61 @@ impl SField {
     }
 
     #[inline(always)]
-    fn set(&mut self, nr: usize) {
+    fn set(&mut self, nr: u8) {
         self.field[self.pos] = nr;
-        self.pos_last_placed = self.pos;
     }
 
     #[inline(always)]
-    fn get_row(&self, row: &mut [usize; 9]) {
+    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 / self.size) * self.size + idx);
+            *row_elem = self.get_field_at_pos((self.pos / SIZE) * SIZE + idx);
         }
     }
 
     #[inline(always)]
-    fn get_col(&self, col: &mut [usize; 9]) {
+    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 * self.size + self.pos % self.size);
+            *col_elem = self.get_field_at_pos(idx * SIZE + self.pos % SIZE);
         }
     }
 
     #[inline(always)]
-    fn get_block(&self, block: &mut [usize; 9]) {
-        let block_start_row = self.pos / self.size / self.block_size * self.block_size;
-        let block_start_col = self.pos % self.size / self.block_size * self.block_size;
+    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..self.block_size {
-            for c in 0..self.block_size {
-                block[r * self.block_size + c] =
-                    self.get_field_at_pos(self.size * (block_start_row + r) + block_start_col + c);
+        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);
             }
         }
     }
 
     #[inline(always)]
-    fn block_ok(&self, nr: usize) -> bool {
-        let mut block = [0; 9];
+    fn block_ok(&self, nr: u8) -> bool {
+        let mut block = [0; SIZE];
         self.get_block(&mut block);
         !block.contains(&nr)
     }
 
     #[inline(always)]
-    fn row_ok(&self, nr: usize) -> bool {
-        let mut row = [0; 9];
+    fn row_ok(&self, nr: u8) -> bool {
+        let mut row = [0; SIZE];
         self.get_row(&mut row);
         !row.contains(&nr)
     }
 
     #[inline(always)]
-    fn col_ok(&self, nr: usize) -> bool {
-        let mut col = [0; 9];
+    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 {
+        if self.pos == NUM_FIELDS - 1 {
             return false;
         }
 
@@ -401,14 +323,16 @@ impl SField {
 
     #[inline(always)]
     fn solve(&mut self) {
+        let now = Instant::now();
         if !self.solve_backtracking() {
             println!("there is no solution.");
         }
+        eprintln!("took {:.3}s", now.elapsed().as_secs_f64());
     }
 }
 
 fn run() -> Result<(), String> {
-    let mut field = SField::new(3);
+    let mut field = SField::new();
 
     field.build_possible_values_db();