题目
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.
解题思路
dfs求两个子树的深度，直径为两个子树的深度和
代码
class Solution:
def diameterOfBinaryTree(self, root: Optional[TreeNode]) -> int:
def dfs(root):
l = r = 0
if root.left:
l = dfs(root.left)
if root.right:
r = dfs(root.right)
self.res = max(self.res, l + r + 1)
return max(l, r) + 1
self.res = 0
dfs(root)
return self.res - 1
