Python递归实现n皇后问题

def solveNQueens(n):
    # 初始化棋盘
    chessboard = [-1] * n
    # 定义 check 函数，判断当前位置是否可放置皇后
    def check(row, col):
        for i in range(row):
            if chessboard[i] == col or \
                abs(row - i) == abs(col - chessboard[i]):
                return False
        return True
    # 定义 backtrack 函数，检查每一行可行的位置，并递归搜索下一行
    def backtrack(row):
        if row == n:
            # 找到一组解法
            res.append(chessboard[:])
            return
        for col in range(n):
            if check(row, col):
                chessboard[row] = col
                backtrack(row+1)
                chessboard[row] = -1
    # 执行回溯算法
    res = []
    backtrack(0)
    # 格式化输出结果
    result = []
    for sol in res:
        cur_res = []
        for i in range(n):
            row_res = "." * sol[i] + "Q" + "." * (n - sol[i] - 1)
            cur_res.append(row_res)
        result.append(cur_res)
    return result