52. N-Queens II

https://leetcode.com/problems/n-queens-ii/description/
题意:还是n皇后,与51题不同的是这里要输出结果总数,而不是结果如何。

思路:回溯,每次找到的时候计数器+1即可。这里计数器要用一个全局的计数器,而不是作为递归参数,否则会遗失。

class Solution:
    count = 0  #全局变量计数器
    def totalNQueens(self, n):
        """
        :type n: int
        :rtype: int
        """
        #self.count = 0  #也可以在这里设置类的全局变量
        board = [['.'] * n for _ in range(n)]
        self.solve(board, 0, n)
        return self.count  #返回计数器

    def solve(self, board, row, n):
        if row == n:  #找到一个结果
            self.count += 1  #注意类变量的使用
        else:
            for col in range(n):
                if self.isValid(board, row, col, n):
                    board[row][col] = 'Q'
                    self.solve(board, row + 1, n)
                    board[row][col] = '.'

    def isValid(self, board, row, col, n):
        for i in range(n):
            if board[i][col] == 'Q':
                return False
        for i, j in zip(range(row - 1, -1, -1), range(col - 1, -1, -1)):
            if board[i][j] == 'Q':
                return False
        for i, j in zip(range(row - 1, -1, -1), range(col + 1, n)):
            if board[i][j] == 'Q':
                return False
        return True

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转载自blog.csdn.net/u012033124/article/details/80696797
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