leetcode题解52：N皇后 II

描述

分析

思路和第51题一样，只不过不是输出数组，而是计数

代码

python

```python class Solution: def totalNQueens(self, n: int) -> int: self.ans = 0 self.dfs([], n) return self.ans

def dfs(self, all_cols, n):
    for c in self.find_candidates(all_cols, n):
        all_cols.append(c)
        if len(all_cols) == n:
            self.ans += 1

        self.dfs(all_cols, n)
        all_cols.pop()

def find_candidates(self, all_cols, n):
    all_valid = []
    for i in range(n):
        if self.isvalid(all_cols, i):
            all_valid.append(i)
    return all_valid

def isvalid(self, all_cols, col):
    row = len(all_cols)
    for r, c in enumerate(all_cols):
        if c == col or abs(row - r) == abs(col - c):
            return False
    return True