N-Queens II

Link:http://oj.leetcode.com/problems/n-queens-ii/

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

 1 public class Solution {
 2     public int num = 0;
 3     public int totalNQueens(int n) {
 4         if (n < 1)
 5             return 0;
 6         num = 0;
 7         int[] queens = new int[n + 1];
 8         for (int i = 1; i <= n; i++) {
 9             queens[1] = i;
10             dfs(2, n, queens);
11         }
12         return num;
13     }
14     public void dfs(int col, int size, int[] queens) {
15         if (col > size) {
16             num++;
17             return;
18         }
19         // here i means row number;
20         for (int i = 1; i <= size; i++) {
21             if (isValid(i, col, queens)) {
22                 queens[col] = i;
23                 dfs(col + 1, size, queens);
24                 queens[col] = 0;
25             }
26         }
27     }
28 
29     public boolean isValid(int row, int col, int[] queens) {
30         for (int i = 1; i < col; i++) {
31             // queens should not be in the same row,
32             // queens should not be placed in the duijiaoxian...
33             // which means |x1-x2|==|y1-y2|
34             if (queens[i] != 0
35                     && (queens[i] == row || (Math.abs(i - col) == Math
36                             .abs(queens[i] - row))))
37                 return false;
38         }
39         return true;
40     }
41 }

 

posted on 2014-05-07 09:09  Atlas-Zzz  阅读(164)  评论(0)  编辑  收藏  举报

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