LeetCode N-Queens

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又是一个八皇后问题：

Given an integer n, return all distinct solutions to the n-queens puzzle.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space respectively.

For example,
There exist two distinct solutions to the 4-queens puzzle:

[ [".Q..",  // Solution 1  "...Q",  "Q...",  "..Q."], ["..Q.",  // Solution 2  "Q...",  "...Q",  ".Q.."]]

class Solution {public:    vector<vector<string> > solveNQueens(int n) {        this->N=n;        memset(matrix,0,sizeof(matrix));        dfs(0);        return d;    }    int check(int x,int y)        {            for(int j=0;j<y;++j)                if(matrix[x][j]==1)return 0;            for(int i=0;i<N;++i)                for(int j=0;j<y;++j)                {                    if(abs(i-x)==abs(j-y)&&matrix[i][j]==1)return 0;                }            return 1;        }    void dfs(int j)        {            if(j==N)            {                //存储                vector<string>mt;                for(int i=0;i<N;++i){                    string td;                    for(int j=0;j<N;++j)                    {                        if(matrix[i][j]==0)td+='.';                        if(matrix[i][j]==1)td+='Q';                    }                    mt.push_back(td);                }                d.push_back(mt);                return ;            }            for(int i=0;i<N;++i)            {                if(matrix[i][j]==0&&check(i,j))                {                    matrix[i][j]=1;                    dfs(j+1);                    matrix[i][j]=0;                }            }        }private :    int N;    vector<vector<string> > d;    int matrix[100][100];};

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