【LeetCode 104_二叉树_遍历】Maximum Depth of Binary Tree

解法一：递归

 int maxDepth(TreeNode* root)
 {
     if (root == NULL)
         return ;

     int max_left_Depth = maxDepth(root->left);
     int max_right_Depth = maxDepth(root->right);
     return max(max_left_Depth, max_right_Depth) + ;
 }

解法二：BFS

 int maxDepth(TreeNode* root)
 {
     if (root == NULL)
         return ;

     queue<TreeNode*> node_queue;
     node_queue.push(root);

     int count = ;
     while (!node_queue.empty()) {
         count++;
         int len = node_queue.size();
         for (int i = ; i < len; ++i) {
             TreeNode *node = node_queue.front();
             node_queue.pop();

             if (node->left)
                 node_queue.push(node->left);
             if (node->right)
                 node_queue.push(node->right);
         }
     }
     return count;
 }