java刷题--51N皇后

Posted 2022-11-29 Anrys

java刷题--51N皇后

• 题目
• 代码
• 结果

题目

代码

class Solution 
    List<List<String>> res = new ArrayList<>();
    public List<List<String>> solveNQueens(int n) 
        char[][] chessboard = new char[n][n];
        for (char[] c : chessboard) 
            Arrays.fill(c, '.');
        
        backTrack(n, 0, chessboard);
        return res;
    
    public void backTrack(int n, int row, char[][] chessboard) 
        if (row == n) 
            res.add(Array2List(chessboard));
            return;
        
        for (int col = 0;col < n; col++) 
            if (isValid (row, col, n, chessboard)) 
                chessboard[row][col] = 'Q';
                backTrack(n, row+1, chessboard);
                chessboard[row][col] = '.';
            
        
    
    public List Array2List(char[][] chessboard) 
        List<String> list = new ArrayList<>();
        for (char[] c : chessboard)  list.add(String.copyValueOf(c));
        return list;
    
    public boolean isValid(int row, int col, int n, char[][] chessboard) 
        // 检查列
        for (int i=0; i<n; ++i) 
            if (chessboard[i][col] == 'Q') 
                return false;
            
        
        // 检查45度对角线
        for (int i=row-1, j=col-1; i>=0 && j>=0; i--, j--) 
            if (chessboard[i][j] == 'Q') 
                return false;
            
        
        // 检查135度对角线
        for (int i=row-1, j=col+1; i>=0 && j<=n-1; i--, j++) 
            if (chessboard[i][j] == 'Q') 
                return false;
            
        return true;
    

结果