117 Diameter-of-a-BT.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:
    int height(TreeNode* root, int &diameter) {
        if(!root)
            return 0;
        
        int lh=height(root->left, diameter);
        int rh=height(root->right, diameter);
        
        diameter=max(diameter,lh+rh);
        return 1+max(lh,rh);
    }
    
    int diameterOfBinaryTree(TreeNode* root) {
        if(root==NULL)
            return 0;
        
        int diameter=0;
        
        height(root,diameter);
        
        return diameter;
    }
};