leetcode-543. Diameter of Binary Tree

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].

class Solution {
public:
    int sumpath = 0;

    int diameterOfBinaryTree(TreeNode* root) {
        dfs(root);
        return sumpath;

    }

    int dfs(TreeNode* root){
        if(root == NULL) return 0;
        int leftpath = dfs(root->left);
        int rightpath =dfs(root->right);
        if(leftpath + rightpath > sumpath)
            sumpath = leftpath + rightpath;
         return max(leftpath +1, rightpath + 1);
    }
};