<p>Given the <code>root</code> of a binary tree, return <em>the length of the <strong>diameter</strong> of the tree</em>.</p>

<p>The <strong>diameter</strong> of a binary tree is the <strong>length</strong> of the longest path between any two nodes in a tree. This path may or may not pass through the <code>root</code>.</p>

<p>The <strong>length</strong> of a path between two nodes is represented by the number of edges between them.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/06/diamtree.jpg" style="width: 292px; height: 302px;" />
<pre>
<strong>Input:</strong> root = [1,2,3,4,5]
<strong>Output:</strong> 3
<strong>Explanation:</strong> 3 is the length of the path [4,2,1,3] or [5,2,1,3].
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> root = [1,2]
<strong>Output:</strong> 1
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 10<sup>4</sup>]</code>.</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</code></li>
</ul>


class Solution {
public:
    int levels(TreeNode*root){
    if(root==NULL)return 0;
    return 1 + max(levels(root->left),levels(root->right));
}
    void helper(TreeNode*root, int &maxDia){
         if(root==NULL)return;
        int ans = levels(root->left)+levels(root->right);
        maxDia = max(maxDia,ans);
        helper(root->left,maxDia);
        helper(root->right,maxDia);
    }
    int diameterOfBinaryTree(TreeNode* root) {
        int maxDia = 0;
        helper(root,maxDia);
        return maxDia;
    }
};
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