LeetCode [543] Diameter of Binary Tree

Given a binary tree, you need to compute 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.

Example:
Given a binary tree 

          1
         / \
        2   3
       / \     
      4   5    

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.

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/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { int ret = 0; public: int diameterOfBinaryTree(TreeNode* root) { helper(root); return ret; } //max len from leaf to node int helper(TreeNode* node){ if(!node) return 0; int left = helper(node->left); int right = helper(node->right); ret = max(ret, left+right); return max(left, right) +1; } };