LeetCode-in-All

543. Diameter of Binary Tree

Easy

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:

Solution

/**
 * 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 {
private:
    int diameter;

public:
    int diameterOfBinaryTree(TreeNode* root) {
        diameter = 0;
        diameterOfBinaryTreeUtil(root);
        return diameter;
    }

private:
    int diameterOfBinaryTreeUtil(TreeNode* root) {
        if (root == nullptr) {
            return 0;
        }
        int leftLength = root->left != nullptr ? 1 + diameterOfBinaryTreeUtil(root->left) : 0;
        int rightLength = root->right != nullptr ? 1 + diameterOfBinaryTreeUtil(root->right) : 0;
        diameter = max(diameter, leftLength + rightLength);
        return max(leftLength, rightLength);
    }
};