LeetCode: 52. N-Queens II

class Solution:
    def totalNQueens(self, n: int) -> int:
        self.ret = 0
        self.solver(n, [], [], [])
        return self.ret
    
    def solver(self, n, queens, sumyx, subyx):
        if len(queens) == n:
            self.ret += 1
            return
        for i in range(n):
            y, x = len(queens), i
            if (i not in queens) and ((y+x) not in sumyx) and ((y-x) not in subyx):
                self.solver(n, queens+[i], sumyx+[(y+x)], subyx+[(y-x)])