Leetcode.37. 解数独

37. 解数独

难度：hard

 对于二维数组的每一位需要从1遍历到9；

 Java：

class Solution {
    public void solveSudoku(char[][] board) {
        backtracking(board);
    }

    public boolean backtracking(char[][] board) {
        for (int i = 0; i < board.length; i++) {
            for (int j = 0; j < board[0].length; j++) {
                if (board[i][j] != '.') {
                    continue;
                }
                for (char k = '1'; k <= '9'; k++) {
                    if (isValid(board, i, j, k)) {
                        board[i][j] = k;
                        if (backtracking(board)) {
                            return true;
                        }
                        board[i][j] = '.';
                    }
                }
                return false;
            }
        }
        return true;
    }

    public boolean isValid(char[][] board, int i, int j, char val) {
        // 行
        for (int k = 0; k < 9; k++) {
            if (board[i][k] == val) {
                return false;
            }
        }
        // 列
        for (int k = 0; k < 9; k++) {
            if (board[k][j] == val) {
                return false;
            }
         }
        // 3*3宫
        // 定位宫格最左上角的元素的坐标
        int row = i / 3 * 3;
        int col = j / 3 * 3;
        for (int i2 = 0; i2 < 3; i2++) {
            for (int j2 = 0; j2 < 3; j2++) {
                if (board[row + i2][col + j2] == val) 
                return false;
            }
        }
        return true;
    }
}

失败代码：

class Solution {
    int i = 0;
    int j = 0;
    public void solveSudoku(char[][] board) {
        backtracking(board);
    }

    public boolean backtracking(char[][] board) {
        if (i == 9 && j == 9) {
            return true;
        }
        if (board[i][j] == '.') {
            for (char k = '1'; k <= '9'; k++) {
                if (isValid(board, i, j, k)) {
                    board[i][j] = k; 
                    int tem1 = i;
                    int tem2 = j;
                    if (j == 8) {
                        j = 0;
                        i++;
                    } else {
                        j++;
                    }
                    if (backtracking(board)) {
                        return true;
                    }
                    board[i][j] = '.';
                    i = tem1;
                    j = tem2;
                }
            }
            return false;
        }
        return true;
        // for (int i = 0; i < board.length; i++) {
        //     for (int j = 0; j < board[0].length; j++) {
        //         if (board[i][j] != '.') {
        //             continue;
        //         }
        //         for (char k = '1'; k <= '9'; k++) {
        //             if (isValid(board, i, j, k)) {
        //                 board[i][j] = k;
        //                 if (backtracking(board)) {
        //                     return true;
        //                 }
        //                 board[i][j] = '.';
        //             }
        //         }
        //         return false;
        //     }
        // }
        // return true;
    }

    public boolean isValid(char[][] board, int i, int j, char val) {
        // 行
        for (int k = 0; k < 9; k++) {
            if (board[i][k] == val) {
                return false;
            }
        }
        // 列
        for (int k = 0; k < 9; k++) {
            if (board[k][j] == val) {
                return false;
            }
         }
        // 3*3宫
        // 定位宫格最左上角的元素的坐标
        int row = i / 3 * 3;
        int col = j / 3 * 3;
        for (int i2 = 0; i2 < 3; i2++) {
            for (int j2 = 0; j2 < 3; j2++) {
                if (board[row + i2][col + j2] == val) 
                return false;
            }
        }
        return true;
    }
}