52. N-Queens II

这一题跟1一样，比1简单一点，只需要个数就可以了

class Solution(object):
    def totalNQueens(self, n):
        """
        :type n: int
        :rtype: int
        """
        board = [['.' for i in range(n)] for j in range(n)]
        res = [0]
        self.dfs(board, 0, res)
        return res[0]
    def dfs(self, board, curcol, res):
        if curcol == len(board):
            res[0] += 1
        for i in range(len(board)):
            if self.check(i, curcol, board):
                board[i][curcol] = 'Q'
                self.dfs(board, curcol+1, res)
                board[i][curcol] = '.'
    def check(self, x, y, board):
        for i in range(len(board)):
            for j in range(y):
                if board[i][j] == 'Q' and ((x+j == y+i) or (x+y == i+j) or (x == i)):
                    return False
        return True