104 Maximum Depth of Binary Tree

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

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


struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

/*
 * Recursive call stack will build towards the maximum depth of the left subtree,
 * and then the right subtree. Leaving the call stack will return the right 
 * subtree tree and then left bottom up.
*/

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