# 543. Diameter of Binary Tree 二叉树的直径

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.

``````/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int diameterOfBinaryTree(TreeNode* root) {
if(root == nullptr) return 0;
int res = depth(root->left) + depth(root->right);
return max(res, max(diameterOfBinaryTree(root->left), diameterOfBinaryTree(root->right)));
}
private:
int depth(TreeNode* root){
if(root == nullptr) return 0;
return 1 + max(depth(root->left), depth(root->right));
}
};
``````