leetcode：N-Queens II

求出N*N棋盘有多少种不同方法放置，跟N-Queue1 一样，只是不需要输出样本

public class Solution {
    static int total = 0;
    public int totalNQueens(int n) {
        number = new int[n + 1];
        for(int i = 0; i < number.length; ++i){
            number[i] = i;
        }
        total = 0;
        dfs(1);
        return total;
    }
    static int[] number;
      void dfs(int cur) {
            if (cur == number.length) {
               ++total;
            } else {
                for (int i = cur; i < number.length; ++i) {
                    swap(number, cur, i);
                    if (isCan(cur)) {
                        dfs(cur + 1);
                    }
                    swap(number, cur, i);
                }
            }
        }

        void swap(int[] a, int i, int j) {
            int t = a[i];
            a[i] = a[j];
            a[j] = t;
        }

        boolean isCan(int cur) {
            for (int i = 1; i < cur; ++i) {
                if ((cur - i) == Math.abs(number[cur] - number[i])) {
                    return false;
                }
            }
            return true;
        }
}