题目：
题解：
class Solution:
def totalNQueens(self, n: int) -> int:
def backtrack(row: int) -> int:
if row == n:
return 1
else:
count = 0
for i in range(n):
if i in columns or row - i in diagonal1 or row + i in diagonal2:
continue
columns.add(i)
diagonal1.add(row - i)
diagonal2.add(row + i)
count += backtrack(row + 1)
columns.remove(i)
diagonal1.remove(row - i)
diagonal2.remove(row + i)
return count
columns = set()
diagonal1 = set()
diagonal2 = set()
return backtrack(0)
