Leetcode 3319. K-th Largest Perfect Subtree Size in Binary Tree

• [Leetcode 3319. K-th Largest Perfect Subtree Size in Binary Tree](#Leetcode 3319. K-th Largest Perfect Subtree Size in Binary Tree)
  • [1. 解题思路](#1. 解题思路)
  • [2. 代码实现](#2. 代码实现)

• 题目链接：3319. K-th Largest Perfect Subtree Size in Binary Tree

1. 解题思路

这一题其实就是一个很常见的树的遍历，我们自底向上遍历每一个子树，看看其是否是完美二叉树，然后如果是的话将其结果存储下来然后找出第k大的结果即可。

2. 代码实现

给出python代码实现如下：

class Solution:
    def kthLargestPerfectSubtree(self, root: Optional[TreeNode], k: int) -> int:
        perfect_subtree = []
        
        def dfs(root):
            nonlocal perfect_subtree
            if root is None:
                return True, 0
            left_is_perfect, left_cnt = dfs(root.left)
            right_is_perfect, right_cnt = dfs(root.right)
            if left_is_perfect and right_is_perfect and left_cnt == right_cnt:
                perfect_subtree.append(left_cnt + right_cnt + 1)
                return True, left_cnt + right_cnt + 1
            else:
                return False, left_cnt + right_cnt + 1
            
        dfs(root)
        perfect_subtree = sorted(perfect_subtree, reverse=True)
        return perfect_subtree[k-1] if len(perfect_subtree) >= k else -1

提交代码评测得到：耗时129ms，占用内存17.3MB。