N-Queens

最新推荐文章于 2025-05-30 23:37:00 发布

原创最新推荐文章于 2025-05-30 23:37:00 发布 · 380 阅读

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class Solution {
public:
    bool isValid (vector<string> &board, int r, int c) {
        for (int i=0; i<board.size(); i++) {
            if (i!=r && board[i][c]=='Q') return false;
            if (i!=c && board[r][i]=='Q') return false;
        }
        for (int i=0; i<board.size(); i++) {
            for (int j=0; j<board.size(); j++) {
                if (i!=r && j!=c) {
                    if (abs(i-r)==abs(j-c) && board[i][j]=='Q') return false;
                }
            }
        }
        return true;
    }
    
    bool dfs(int r, int n, vector<vector<string> > &res, vector<string> &cur) {
        if (r==n) {
            res.push_back(cur);
            return true;
        }
        for (int c=0; c<n; c++) {
            cur[r][c]='Q';
            if (isValid(cur, r, c)) {
                dfs (r+1, n, res, cur);
            }
            cur[r][c]='.';
        }
        return false;
    }
    
    vector<vector<string> > solveNQueens(int n) {
        string p(n,'.');
        vector<string> cur(n, p);
        vector<vector<string> > res;
        dfs(0,n,res,cur);
        return res;
    }
};

II:

class Solution {
public:
    bool isValid (vector<string> &board, int r, int c) {  
        for (int i=0; i<board.size(); i++) {  
            if (i!=r && board[i][c]=='Q') return false;  
            if (i!=c && board[r][i]=='Q') return false;  
        }  
        for (int i=0; i<board.size(); i++) {  
            for (int j=0; j<board.size(); j++) {  
                if (i!=r && j!=c) {  
                    if (abs(i-r)==abs(j-c) && board[i][j]=='Q') return false;  
                }  
            }  
        }  
        return true;  
    }  
      
    bool dfs(int r, int n, int &res, vector<string> &cur) {  
        if (r==n) {  
            res++;  
            return true;  
        }  
        for (int c=0; c<n; c++) {  
            cur[r][c]='Q';  
            if (isValid(cur, r, c)) {  
                dfs (r+1, n, res, cur);  
            }  
            cur[r][c]='.';  
        }  
        return false;  
    }
    int totalNQueens(int n) {
        int res=0;
        string p(n,'.');  
        vector<string> cur(n, p);  
        dfs(0,n,res,cur);  
        return res;
    }
};