/**
 * 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 {
private:
    int height(TreeNode* node, int& diameter)//그대로 사용
    {
        if(!node)
            return 0;
        int l = height(node->left, diameter);
        int r = height(node->right, diameter);
        diameter = max(diameter,l+r);
        return 1+max(l,r);
    }

public:
    int diameterOfBinaryTree(TreeNode* root) {
        int diameter = 0;
        height(root,diameter);
        return diameter;

    }
};