【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 0;

    int max_left_Depth = maxDepth(root->left);
    int max_right_Depth = maxDepth(root->right);
    return max(max_left_Depth, max_right_Depth) + 1;
}

解法二：BFS

int maxDepth(TreeNode* root)
{
    if (root == NULL)
        return 0;

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

    int count = 0;
    while (!node_queue.empty()) {
        count++;
        int len = node_queue.size();
        for (int i = 0; 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;
}