solve 37

Author: Zhang Xiaodong

src/solution/mod.rs

@@ -32,3 +32,4 @@ mod s0033_search_in_rotated_sorted_array;
 mod s0034_find_first_and_last_position_of_element_in_sorted_array;
 mod s0035_search_insert_position;
 mod s0036_valid_sudoku;
+mod s0037_sudoku_solver;

src/solution/s0037_sudoku_solver.rs

@@ -0,0 +1,148 @@
+/**
+ * [37] 解数独
+ *
+ * 编写一个程序，通过填充空格来解决数独问题。
+ * 数独的解法需 遵循如下规则：
+ * <ol>
+ * 	数字 1-9 在每一行只能出现一次。
+ * 	数字 1-9 在每一列只能出现一次。
+ * 	数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。（请参考示例图）
+ * </ol>
+ * 数独部分空格内已填入了数字，空白格用 '.' 表示。
+ *  
+ * <div class="top-view__1vxA">
+ * <div class="original__bRMd">
+ * <div>
+ * 示例 1：
+ * <img src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2021/04/12/250px-sudoku-by-l2g-20050714svg.png" style="height:250px; width:250px" />
+ * 输入：board = [["5","3",".",".","7",".",".",".","."],["6",".",".","1","9","5",".",".","."],[".","9","8",".",".",".",".","6","."],["8",".",".",".","6",".",".",".","3"],["4",".",".","8",".","3",".",".","1"],["7",".",".",".","2",".",".",".","6"],[".","6",".",".",".",".","2","8","."],[".",".",".","4","1","9",".",".","5"],[".",".",".",".","8",".",".","7","9"]]
+ * 输出：[["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],["4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9","6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4","5","2","8","6","1","7","9"]]
+ * 解释：输入的数独如上图所示，唯一有效的解决方案如下所示：
+ * <img src=" https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2021/04/12/250px-sudoku-by-l2g-20050714_solutionsvg.png" style="height:250px; width:250px" />
+ *
+ *  
+ * 提示：
+ *
+ * 	board.length == 9
+ * 	board[i].length == 9
+ * 	board[i][j] 是一位数字或者 '.'
+ * 	题目数据 保证 输入数独仅有一个解
+ * </div>
+ * </div>
+ * </div>
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.cn/problems/sudoku-solver/
+// discuss: https://leetcode.cn/problems/sudoku-solver/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+use std::collections::HashSet;
+
+impl Solution {
+    fn init_sets(board: &mut Vec<Vec<char>>) -> (Vec<HashSet<char>>, Vec<HashSet<char>>, Vec<HashSet<char>>) {
+        let (mut rows, mut cols, mut blks) = (vec![], vec![], vec![]);
+        for j in 0..9 {
+            let mut row = HashSet::new();
+            let mut col = HashSet::new();
+            let mut blk = HashSet::new();
+            rows.push(row);
+            cols.push(col);
+            blks.push(blk);
+        }
+        for i in 0..81 {
+            let (m, n) = (i/9, i%9);
+            let blk_idx = m / 3 * 3 + n / 3;
+            match board[m][n] {
+                '.' => {},
+                c => {
+                    cols[n].insert(c);
+                    rows[m].insert(c);
+                    blks[blk_idx].insert(c);
+                },
+            }
+        }
+        return (rows, cols, blks);
+    }
+
+    pub fn solve_sudoku(board: &mut Vec<Vec<char>>) {
+        let (mut rows, mut cols, mut blks) = Self::init_sets(board);
+        let mut stack = vec![];
+        let mut i = 0;
+        let mut sc = '1';
+
+        'outer: while i < 81 {
+            let (m, n) = (i/9, i%9);
+            let blk_idx = m / 3 * 3 + n / 3;
+            match board[m][n] {
+                '.' => {
+                    let mut found = false;
+                    for c in sc..='9' {
+                        if rows[m].contains(&c) || cols[n].contains(&c) || blks[blk_idx].contains(&c) {
+                            continue;
+                        }
+                        board[m][n] = c;
+
+                        rows[m].insert(c);
+                        cols[n].insert(c);
+                        blks[blk_idx].insert(c);
+
+                        stack.push((i, c));
+                        found = true;
+                        break;
+                    }
+                    if !found {
+                        (i, sc) = stack.pop().unwrap();
+                        let (m, n) = (i/9, i%9);
+                        let blk_idx = m / 3 * 3 + n / 3;
+                        board[m][n] = '.';
+                        rows[m].remove(&sc);
+                        cols[n].remove(&sc);
+                        blks[blk_idx].remove(&sc);
+                        sc = (sc as u8 + 1) as char;
+                        continue 'outer;
+                    }
+                },
+                _ => {},
+            }
+            sc = '1';
+            i += 1;
+        }
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_37() {
+        let mut board = vec![
+            vec!['5','3','.','.','7','.','.','.','.'],
+            vec!['6','.','.','1','9','5','.','.','.'],
+            vec!['.','9','8','.','.','.','.','6','.'],
+            vec!['8','.','.','.','6','.','.','.','3'],
+            vec!['4','.','.','8','.','3','.','.','1'],
+            vec!['7','.','.','.','2','.','.','.','6'],
+            vec!['.','6','.','.','.','.','2','8','.'],
+            vec!['.','.','.','4','1','9','.','.','5'],
+            vec!['.','.','.','.','8','.','.','7','9'],
+        ];
+        Solution::solve_sudoku(&mut board);
+        assert_eq!(board, vec![
+            vec!['5','3','4','6','7','8','9','1','2'],
+            vec!['6','7','2','1','9','5','3','4','8'],
+            vec!['1','9','8','3','4','2','5','6','7'],
+            vec!['8','5','9','7','6','1','4','2','3'],
+            vec!['4','2','6','8','5','3','7','9','1'],
+            vec!['7','1','3','9','2','4','8','5','6'],
+            vec!['9','6','1','5','3','7','2','8','4'],
+            vec!['2','8','7','4','1','9','6','3','5'],
+            vec!['3','4','5','2','8','6','1','7','9'],
+        ]);
+    }
+}