[leetcode] 37. 解数独(Java)(dfs,递归,回溯)

37. 解数独

1A

这个题其实15分钟左右就敲出来并且对了。。。但是由于我输错了一个数。。导致我白白debug一个多小时。。

没啥难度，练递归-dfs的好题

class Solution {

    private int which(int i, int j) {

        if (i <= 2) {

            if (j <= 2)

                return 1;

            if (j <= 5)

                return 2;

            return 3;

        }

        if (i <= 5) {

            if (j <= 2)

                return 4;

            if (j <= 5)

                return 5;

            return 6;

        }

        if (j <= 2)

            return 7;

        if (j <= 5)

            return 8;

        return 9;

    }

    public void solveSudoku(char[][] board) {

        int[][] k = new int[10][10];

        // heng

        int[][] p = new int[10][10];

        // shu

        int[][] q = new int[10][10];

        for (int i = 0; i < 9; i++) {

            for (int j = 0; j < 9; j++) {

                if (board[i][j] != '.') {

                    p[i][board[i][j] - '0'] = 1;

                    q[j][board[i][j] - '0'] = 1;

                    k[which(i, j)][board[i][j] - '0'] = 1;

                }

            }

        }

        dfs(k, p, q, board, 0, 0);

    }

    private boolean dfs(int[][] k, int[][] p, int[][] q, char[][] board, int i, int j) {

        if (j == 9) return true;

        if (board[i][j] != '.') {

            if (i + 1 < 9) {

                boolean rst = dfs(k, p, q, board, i + 1, j);

                if (rst) {

                    return true;

                }

            } else {

                boolean rst = dfs(k, p, q, board, 0, j + 1);

                if (rst) {

                    return true;

                }

            }

        } else {

            for (int x = 1; x <= 9; x++) {

                if (p[i][x] != 1 && q[j][x] != 1 && k[which(i, j)][x] != 1) {

                    p[i][x] = 1;

                    q[j][x] = 1;

                    k[which(i, j)][x] = 1;

                    board[i][j] = (char) (x + '0');

                    if (i + 1 < 9) {

                        boolean rst = dfs(k, p, q, board, i + 1, j);

                        if (rst) {

                            return true;

                        }

                    } else {

                        boolean rst = dfs(k, p, q, board, 0, j + 1);

                        if (rst) {

                            return true;

                        }

                    }

                    p[i][x] = 0;

                    q[j][x] = 0;

                    k[which(i, j)][x] = 0;

                    board[i][j] = '.';

                }

            }

        }

        return false;

    }

}

[leetcode] 37. 解数独(Java)(dfs,递归,回溯)的相关教程结束。