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.

/**

 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:

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

    int maxDepth(TreeNode *root) {
          
        int maximum = maxDepthHelper(root);
        
        return maximum;
            
    }
};