Leetcode:52. N-QueensII

Description

Follow up for N-Queens problem.

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

思路

• 递归方式
• 主要是要判断当前位置是否是合理位置，参考isValid函数

代码

class Solution {
public:
    int totalNQueens(int n) {
        int res = 0;
        if(n == 0) return 0;
        
        vector<string> flag(n, string(n, '.'));
        getResult(flag, n, 0, res);
        
        return res;
    }
    
    void getResult(vector<string> &flag, int n, int rows, int &res){
        if(rows == n){
            res++;
            return;
        }
        else{
            for(int i = 0; i < n; ++i){
                if(isValid(flag, rows, i, n)){
                    flag[rows][i] = 'Q';
                    getResult(flag, n, rows + 1, res);
                    flag[rows][i] = '.';
                }
            }
        }
    }
    bool isValid(vector<string> &nums, int rows, int cols, int n){
        for(int i = 0; i < rows; ++i)
            if(nums[i][cols] == 'Q') return false;
            
        for(int i = rows - 1, j = cols - 1; i >= 0 && j >= 0; --i, --j)
            if(nums[i][j] == 'Q') return false;
            
        for(int i = rows - 1, j = cols + 1; i >= 0 && j < n; --i, ++j)
            if(nums[i][j] == 'Q') return false;
            
        return true;
    }
};