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.

My code of C++, Depth-first-search and Breadth-first-searchDepth-first-search======Only one line code.int maxDepth(TreeNode *root){    return root == NULL ? 0 : max(maxDepth(root -> left), maxDepth(root -> right)) + 1;}Breadth-first-search======Calculate the count of the last level.int maxDepth(TreeNode *root){    if(root == NULL)        return 0;        int res = 0;    queue<TreeNode *> q;    q.push(root);    while(!q.empty())    {        ++ res;        for(int i = 0, n = q.size(); i < n; ++ i)        {            TreeNode *p = q.front();            q.pop();                        if(p -> left != NULL)                q.push(p -> left);            if(p -> right != NULL)                q.push(p -> right);        }    }        return res;}