题解 | #N皇后问题#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param n int整型 the n
     * @return int整型
     */
    Integer num = 0;
    int[][] isVisited;
    public int Nqueen (int n) {
        // write code here
        isVisited = new int[n][n];
        solution3(n, 0, -2);
        return num;
    }
    public void solution3(int n, int column, int preLine) {
        if (column == n) {
            num++;
            return;
        }
        for (int i = 0; i < n; i++) {
            if (isVisited[column][i] > 0 || i == preLine - 1 || i == preLine + 1 ||
                    i == preLine) {
                continue;
            } else {
                isVisited[column][i]++;
                for (int k = column + 1; k < n; k++) {
                    isVisited[k][i]++;
                }
                int zl = i - 1, yl = i + 1, hang = column + 1;
                while (zl >= 0 && hang < n) {
                    isVisited[hang++][zl--]++;
                }
                hang = column + 1;
                while (yl < n && hang < n) {
                    isVisited[hang++][yl++]++;
                }
                solution3(n, column + 1, i);
                isVisited[column][i]--;
                zl = i - 1;
                yl = i + 1;
                hang = column + 1;
                while (zl >= 0 && hang < n) {
                    isVisited[hang++][zl--]--;
                }
                hang = column + 1;
                while (yl < n && hang < n) {
                    isVisited[hang++][yl++]--;
                }
                for (int k = column + 1; k < n; k++) {
                    isVisited[k][i]--;
                }
            }
        }
    }
}