solution.cpp

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