543. Diameter of Binary Tree

/**

• 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 max_=0;
  int diameterOfBinaryTree(TreeNode root) {
  if (!root) return 0;
  int res = helper(root->left) + helper(root->right);
  return max(res, max(diameterOfBinaryTree(root->left), diameterOfBinaryTree(root->right)));
  }
  int helper(TreeNode* root){
  if(!root)return 0;
  return 1+max(helper(root->left),helper(root->right));
  }
  };