## 题目描述：

LeetCode 543. Diameter of Binary Tree

Given a binary tree, you need to compute 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.

Example:
Given a binary tree

```          1
/ \
2   3
/ \
4   5
```

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.

## Python代码：

``````# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def traverse(self, root):
if not root: return 0
left = self.traverse(root.left)
right = self.traverse(root.right)
self.ans = max(self.ans, left + right)
return max(left, right) + 1

def diameterOfBinaryTree(self, root):
"""
:type root: TreeNode
:rtype: int
"""
self.ans = 0
self.traverse(root)
return self.ans
``````

## Python代码：

``````# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def depth(self, root):
if not root: return 0
return 1 + max(self.depth(root.left), self.depth(root.right))

def traverse(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if not root: return 0
return max(self.depth(root.left) + 1 + self.depth(root.right), \
self.traverse(root.left), \
self.traverse(root.right))

def diameterOfBinaryTree(self, root):
"""
:type root: TreeNode
:rtype: int
"""
return max(self.traverse(root) - 1, 0)
``````

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