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LeetCode 543 Diameter of a Binary Tree in C++

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:

-100 <= Node.val <= 100

The number of nodes in the tree is in the range [1, 104].

Solution in C++ with a test case:


#include <iostream>
#include <algorithm>
using namespace std;

// 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 {
public:
    int result;
    int dfs(TreeNode* root) {
        if (root == nullptr) return 0;
        int left = dfs(root->left);
        int right = dfs(root->right);
        result = max(result, left + right);
        return max(left, right) + 1;
    }

    int diameterOfBinaryTree(TreeNode* root) {
        result = 0;
        dfs(root);
        return result;
    }
};

// Helper function to create a tree
TreeNode* createTree() {
    /*
        Example tree:
                1
               / \
              2   3
             / \
            4   5
    */
    TreeNode* root = new TreeNode(1);
    root->left = new TreeNode(2);
    root->right = new TreeNode(3);
    root->left->left = new TreeNode(4);
    root->left->right = new TreeNode(5);
    return root;
}

int main() {
    // Create a sample binary tree
    TreeNode* root = createTree();

    // Create a Solution object
    Solution solution;

    // Call the diameterOfBinaryTree function
    int diameter = solution.diameterOfBinaryTree(root);

    // Output the result
    cout << "Diameter of the binary tree: " << diameter << endl;

    // Clean up memory (optional but good practice)
    delete root->left->left;
    delete root->left->right;
    delete root->left;
    delete root->right;
    delete root;

    return 0;
}