LCA之朴素求法（例题：HDU2586）

LCA之朴素求法

最近公共祖先简称 LCA（Lowest Common Ancestor）。两个节点的最近公共祖先，就是这两个点的公共祖先里面，离根最远的那个。

求LCA有很多很多的办法，最简单的就是朴素求法：每次找深度比较大的那个点，让它向上跳。显然在树上，这两个点最后一定会相遇，相遇的位置就是想要求的 LCA。
这个极其暴力的做法，复杂度为O(n)，我们来尝试一下吧。

How far away ？

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 31166 Accepted Submission(s): 12651

Problem Description

There are n houses in the village and some bidirectional roads connecting them. Every day peole always like to ask like this “How far is it if I want to go from house A to house B”? Usually it hard to answer. But luckily int this village the answer is always unique, since the roads are built in the way that there is a unique simple path(“simple” means you can’t visit a place twice) between every two houses. Yout task is to answer