# Diameter of Binary Tree Problem & Solution

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.

## C++ Solution

``````#pragma GCC optimize("Ofast")
#pragma GCC optimization("max-inline-insns-recursive-auto")

static const int _=[](){ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();

/**
* struct TreeNode {
*   int val;
*   TreeNode *left;
*   TreeNode *right;
*   TreeNode() : val(0), left(nullptr), right(nullptr) {}
*   TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
*   TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
int diameterOfBinaryTree(TreeNode* root) {
int result = 0;
diameterOfBinaryTree(root, result);

return result;
}

private:
int diameterOfBinaryTree(TreeNode* root, int& diameter) {
if (root == nullptr) {
return -1;
}

int left = 1 + diameterOfBinaryTree(root->left, diameter);
int right = 1 + diameterOfBinaryTree(root->right, diameter);
diameter = max(diameter, left + right);

return max(left, right);
}
};
``````