0058_P543_Diameter_of_Binary_Tree.cpp

/* 
Day: 58
Problem Number: 543 (https://leetcode.com/problems/diameter-of-binary-tree)
Date: 27-02-2024 
Description:
Given the root of a binary tree, return the length of the diameter of the tree.
The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.
The length of a path between two nodes is represented by the number of edges between them.
 
Example 1:
Input: root = [1,2,3,4,5]
Output: 3
Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3].

Example 2:
Input: root = [1,2]
Output: 1
 
Constraints:
* The number of nodes in the tree is in the range [1, 104].
* -100 <= Node.val <= 100

Code:  */
/**
 * 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 {
public:
    int ans;
    int diameterOfBinaryTree(TreeNode* root) {
        ans = 0;
        dfs(root);
        return ans;
    }

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