题解 | #N皇后问题#

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param n int整型 the n
# @return int整型
#
class Solution:
    def __init__(self):
        self.count = 0
    def Nqueen(self , n: int) -> int:
        # write code here
        rec = set()#被占用列
        rec2 = set()#被占用斜线1
        rec3 = set()#被占用斜线2
        def check(i,j):
            if j in rec or i+j in rec2 or i-j in rec3:
                return False
            return True
        def dfs(index):
            for i in range(index,n):
                for j in range(n):
                    if check(i,j):
                        rec.add(j)
                        rec2.add(i+j)
                        rec3.add(i-j)
                        if dfs(i+1):
                            self.count+=1
                        rec.remove(j)
                        rec2.remove(i+j)
                        rec3.remove(i-j)
                    else:
                        continue
                return False
            return True
        dfs(0)
        return self.count