java刷题--51N皇后

Posted 2021-08-29 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