Java利用深度搜索解决数独游戏详解

package com.platform.modules.alg.alglib.poj2676;
 
public class Poj2676 {
    public String output = "";
    int map[][] = new int[10][10];
    // row[i][x] 标记在第 i 行中数字 x 是否已出现
    boolean row[][] = new boolean[10][10];
    // col[j][y] 标记在第 j 列中数字 y 是否已出现
    boolean col[][] = new boolean[10][10];
    // grid[k][z] 标记在第 k 个 3*3 子格中数字z是否已出现
    boolean grid[][] = new boolean[10][10];
 
    boolean dfs(int i, int j) {
        if (i == 10)
            return true;
        boolean flag;
        if (map[i][j] > 0) {
            if (j == 9)
                flag = dfs(i + 1, 1);
            else
                flag = dfs(i, j + 1);
            return flag ? true : false;
        } else {
            int k = 3 * ((i - 1) / 3) + (j - 1) / 3 + 1;
            for (int x = 1; x <= 9; x++) {//枚举数字1~9填空
                if (!row[i][x] && !col[j][x] && !grid[k][x]) {
                    map[i][j] = x;
                    row[i][x] = true;
                    col[j][x] = true;
                    grid[k][x] = true;
                    if (j == 9)
                        flag = dfs(i + 1, 1);
                    else
                        flag = dfs(i, j + 1);
                    if (!flag) { //回溯，继续枚举
                        map[i][j] = 0;
                        row[i][x] = false;
                        col[j][x] = false;
                        grid[k][x] = false;
                    } else
                        return true;
                }
            }
        }
        return false;
    }
 
    public String cal(String input) {
        String[] line = input.split("\n");
 
 
        char ch;
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= 9; j++) {
                ch = line[i-1].charAt(j-1);
                map[i][j] = ch - '0';
                if (map[i][j] > 0) {
                    int k = 3 * ((i - 1) / 3) + (j - 1) / 3 + 1;
                    row[i][map[i][j]] = true;
                    col[j][map[i][j]] = true;
                    grid[k][map[i][j]] = true;
                }
            }
        }
 
        dfs(1, 1);
        for (int i = 1; i <= 9; i++) {
            for (int j = 1; j <= 9; j++)
                output += map[i][j];
            output += "\n";
        }
        return output;
    }
}