【HDU 2586 How far away ?】

题目链接

http://acm.hdu.edu.cn/showproblem.php?pid=2586

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 all these curious people.

Input

First line is a single integer T(T<=10), indicating the number of test cases.
For each test case,in the first line there are two numbers n(2<=n<=40000) and m (1<=m<=200),the number of houses and the number of queries. The following n-1 lines each consisting three numbers i,j,k, separated bu a single space, meaning that there is a road connecting house i and house j,with length k(0<k<=40000).The houses are labeled from 1 to n.
Next m lines each has distinct integers i and j, you areato answer the distance between house i and house j.

Output

For each test case,output m lines. Each line represents the answer of the query. Output a bland line after each test case.

Sample Input

2
3 2
1 2 10
3 1 15
1 2
2 3

2 2
1 2 100
1 2
2 1

Sample Output

10
25
100
100

LCA模板题,此处用倍增法实现。

以\(1\)号节点为根,设\(dis[x]\)表示\(x\)号节点到\(1\)号节点的距离,则显然答案为:

\(dis[x]+dis[y]-2*dis[LCA(x,y)]\),其中,乘2是因为\(dis[x]\)和\(dis[y]\)计算了两次\(LCA(x,y)\)到根节点的距离。

 

stdKonjac

stdKonjac

一只挣扎的蒟蒻ACMer

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