HDU 2586 How far away ？(lca)

How far away ？

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 8878    Accepted Submission(s): 3087

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 离线模板

/* ***********************************************
Author        :
Created Time  :2015/8/12 13:31:52
File Name     :6.cpp
************************************************ */
#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <stdio.h>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <iomanip>
#include <list>
#include <deque>
#include <stack>
#define ull unsigned long long
#define ll long long
#define mod 90001
#define INF 0x3f3f3f3f
#define maxn 40000+10
#define cle(a) memset(a,0,sizeof(a))
const ull inf = 1LL << 61;
const double eps=1e-5;
using namespace std;

bool cmp(int a,int b){
    return a>b;
}
int fa[maxn],n,m,pre[maxn],l;
int dis[maxn];
int a[300][3];
vector<int>vec[maxn];
struct node{
	int v,next,w;
}edge[2*maxn+100];
map<pair<int,int>,int>mp;
void add(int u,int v,int w){
	edge[l].v=v;
	edge[l].w=w;
	edge[l].next=pre[u];
	pre[u]=l++;
}
int findfa(int x){
	if(x==fa[x])return x;
	else return fa[x]=findfa(fa[x]);
}

void Union(int x,int y){
	x=findfa(x);
	y=findfa(y);
	fa[y]=x;
}
void dfs(int u){
	int	v;
	fa[u]=u;
	for(int i=pre[u];i+1;i=edge[i].next){
		v=edge[i].v;
		if(fa[v]==-1){
			dis[v]=edge[i].w+dis[u];
			dfs(v);
			Union(u,v);
		}
	}
	for(int j=0;j<vec[u].size();j++){
		 v=vec[u][j];
		 if(fa[v]!=-1){
			mp[make_pair(u,v)]=mp[make_pair(v,u)]=dis[v]+dis[u]-2*dis[findfa(v)];
		 }
	}
}
int main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt","r",stdin);
    #endif
	//freopen("out.txt","w",stdout);
    int t;
	cin>>t;
	int x,y,z;
	while(t--){
		scanf("%d%d",&n,&m);
		l=0;
		mp.clear();

		memset(fa,-1,sizeof fa);
		memset(pre,-1,sizeof pre);

		cle(dis);cle(a);
		for(int i=0;i<=n;i++)vec[i].clear();

		for(int i=1;i<n;i++){
			scanf("%d %d %d",&x,&y,&z);
			add(x,y,z);
			add(y,x,z);
		}
		for(int i=1;i<=m;i++){
			scanf("%d %d",&x,&y);
			vec[x].push_back(y);
			vec[y].push_back(x);
			a[i][0]=x;
			a[i][1]=y;
		}
		dfs(1);
		for(int i=1;i<=m;i++){
			printf("%d\n",mp[make_pair(a[i][0],a[i][1])]);
		}
	}
    return 0;
}