543. Diameter of Binary Tree

• Difficulty: Easy

• Topics: Tree

• Similar Questions:

Problem:

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.

Solutions:

/**
 * 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 {
public:
    int diameterOfBinaryTree(TreeNode* root) {
        int depth;
        return helper(root, depth);
    }

private:
    int helper(TreeNode* root, int& depth) {
        if (root == nullptr) {
            depth = 0;
            return 0;
        }

        int leftDepth, rightDepth;
        int left = helper(root->left, leftDepth);
        int right = helper(root->right, rightDepth);

        depth = 1 + max(leftDepth, rightDepth);
        return max(max(left, right), leftDepth + rightDepth);
    }
};