说明：  此文章的算法有迭代法、穷举搜索法、递推法、贪婪法、回溯法、分治法、动态规划法等等，有用的的人可以
(This article has iteration of the algorithm, exhaustive search method, the recursive method, greedy method, backtracking, sub-rule method, dynamic programming, etc., can be useful)