/**
 * 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) {}
 * };
 */
int ans;
int dfs(TreeNode* root)
{
    int l=0,r=0;
    if(root->left!=NULL)
        l = dfs(root->left);
    if(root->right!=NULL)
        r = dfs(root->right);
    ans = max(ans,l+r+1);
    return max(l,r)+1;

}
class Solution {
public:
    int diameterOfBinaryTree(TreeNode* root) {
        ans=0;
        dfs(root);
        return ans-1;
    }
};