time tracking

src/main.rs

@@ -1,3 +1,5 @@
+use std::time::Instant;
+
 struct SField {
     field: Vec<usize>,
     fixed: Vec<usize>,
@@ -401,9 +403,11 @@ impl SField {
 
     #[inline(always)]
     fn solve(&mut self) {
+        let now = Instant::now();
         if !self.solve_backtracking() {
             println!("there is no solution.");
         }
+        println!("took {:.3}s", now.elapsed().as_secs_f64());
     }
 }