diameterOfBinaryTree.cpp

/**
 * Definition for a binary tree node.
 * 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:
    pair<int,int> diameterfast(TreeNode* root, pair<int,int>& ans){
        if(root==NULL){
            pair<int,int> p = make_pair(0,0);
            return p;
        }
        pair<int,int> left = diameterfast(root->left, ans);
        pair<int,int> right = diameterfast(root->right, ans);
    int op1  = left.first;
    int op2 = right.first;
    int op3 = left.second + right.second +1;
    ans.first = max(op1, max(op2, op3));
    ans.second = max(left.second, right.second)+1;
    return ans;
    }
    int diameterOfBinaryTree(TreeNode* root) {
    pair<int,int> ans;
      diameterfast(root, ans);
      return ans.first-1;
    }
};