# 题目描述：

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.

# 代码实现：

``````/**
* 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 dia=0;
int diameterOfBinaryTree(TreeNode* root) {
if(root==nullptr){
return 0;
}
if(root->left==nullptr && root->right==nullptr){
return 0;
}
DepthOfBinaryTree(root);

return dia;
}
private:
int DepthOfBinaryTree(TreeNode* root){
if(!root){
return 0;
}
int left=DepthOfBinaryTree(root->left);
int right=DepthOfBinaryTree(root->right);
dia=max(dia, left+right);
return 1+max(left,right);
}
};
``````