原題鏈接

思路：
簡單bfs

class Solution
{
public:
  int maxDepth(Node *root)
  {
    int depth = 0;
    if (root == NULL)
      return 0;
    queue<Node *> q;
    q.push(root);
    while (q.size() > 0)
    {
      depth++;
      int len = q.size();
      for (int i = 0; i < len; i++)
      {
        vector<Node *> temp = q.front()->children;
        q.pop();
        for (Node *n : temp)
        {
          q.push(n);
        }
      }
    }
    return depth;
  }
};