543. Diameter of Binary Tree

543. Diameter of Binary Tree (Easy)

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.

Related Topics:
Tree

Solution 1. Post-order traversal

// OJ: https://leetcode.com/problems/diameter-of-binary-tree/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(H)
class Solution {
    int ans = 0;
    int postorder(TreeNode *root) {
        if (!root) return 0;
        int left = postorder(root->left), right = postorder(root->right);
        ans = max(ans, left + right);
        return 1 + max(left, right);
    }
public:
    int diameterOfBinaryTree(TreeNode* root) {
        postorder(root);
        return ans;
    }
};