【leetcode刷题笔记】N-Queens II

Follow up for N-Queens problem.

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

---

 

题解：参见http://www.cnblogs.com/sunshineatnoon/p/3853170.html

只要求求出解的个数，稍微改一下代码就可以了：用私有变量result记录解的数目，当搜索到一个解的时候，result+1即可。

代码如下：

public class Solution {
private int result = 0;
    private boolean isValid(List<Integer> cols,int col){
        for(int i = 0;i < cols.size();i++){
            if(cols.get(i) == col)
                return false;
            if(cols.size() - i == Math.abs(cols.get(i) - col))
                return false;
        }
        return true;
    }
    private void QueenDfs(int n,int level,List<Integer> cols){
        if(level == n){
            result++;
        }
        
        for(int i = 0;i < n;i++){
            if(isValid(cols, i)){
                cols.add(i);
                QueenDfs(n, level+1, cols);
                cols.remove(cols.size()-1);
            }
        }
    }
    public int totalNQueens(int n) {

        List<Integer> cols = new ArrayList<Integer>();
        QueenDfs(n, 0, cols );
        
        return result;
    }
}