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.

比较简单，用dfs就行。

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