543. Diameter of Binary Tree_easy.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 {
    /**CORE IDEA: to imply dfs to get the max path 
    max path betn nodes , 1+ max path (l or r)
    **/
public:
    int diameterOfBinaryTree(TreeNode* root) {
        int res=0;
        dfs(root,res);
        return res; 
    }
private:
    int dfs(TreeNode* root,int &res){
        if(root==NULL){
            return 0;
        }
        int left = dfs(root->left,res);
        int right= dfs(root->right,res);

        res=max(res,left+right);
        return 1+max(left,right);
    }
};