LeetCode 104: Maximum Depth of Binary Tree

/**
 * 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 height = 0;
public:
    void findHeight(TreeNode *node, int depth) {
        if(node == NULL) return;
        
        if(depth > height) height = depth;
        
        if(node->left != NULL) findHeight(node->left, depth + 1);
        if(node->right != NULL) findHeight(node->right, depth + 1);
    }
    
    int maxDepth(TreeNode* root) {
        if(root == NULL) return 0;
        
        findHeight(root, 1);
        return height;
    }
};