11. Diameter of Binary Tree.cpp

/*
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
*/
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/**
 * 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 fun(TreeNode*root, int &d) {
        if(root==NULL)
            return 0;
        
        int lt = fun(root->left,d);
        int rt = fun(root->right,d);
        
        d = max(d,lt+rt);
        
        return max(lt,rt)+1;
    }
    
    int diameterOfBinaryTree(TreeNode* root) {
        int d = 0;
        
        fun(root,d);
        
        return d;
    }
};