543. Diameter of Binary Tree
Recursive Tree
Given the root
of a binary tree, return the length of the diameter of the tree.
The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root
.
The length of a path between two nodes is represented by the number of edges between them.
Example 1:
Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].
Example 2:
Input: root = [1,2]
Output: 1
Constraints:
The number of nodes in the tree is in the range
[1, 10
4
]
.-100 <= Node.val <= 100
分析
求最长的线段,# of nodes - 1
递归函数不断更新最长边长,返回高度
from typing import Optional
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
class Solution:
def diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
res = 0
def helper(root):
nonlocal res
if not root:
return 0
left = helper(root.left)
right = helper(root.right)
res = max(res, left + right) #count edges, not nodes
return 1 + max(left, right) #return height(# of nodes)
helper(root)
return res
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