hdu 2586 lca模板题

How far away ？

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4106    Accepted Submission(s): 1567

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

23 21 2 103 1 151 22 32 21 2 1001 22 1

 

Sample Output

1025100100

 

好久没写lca，回顾一下。

代码：

/* ***********************************************Author :rabbitCreated Time :2014/3/29 11:40:24File Name :E.cpp************************************************ */#pragma comment(linker, "/STACK:102400000,102400000")#include <stdio.h>#include <iostream>#include <algorithm>#include <sstream>#include <stdlib.h>#include <string.h>#include <limits.h>#include <string>#include <time.h>#include <math.h>#include <queue>#include <stack>#include <set>#include <map>using namespace std;#define INF 0x3f3f3f3f#define eps 1e-8#define pi acos(-1.0)typedef long long ll;const int maxn=50010;int head[maxn],tol,dis[maxn],fa[maxn][20],dep[maxn];struct node{int next,to,val;}edge[5*maxn];void addedge(int u,int v,int w){edge[tol].to=v;edge[tol].next=head[u];edge[tol].val=w;head[u]=tol++;}void bfs(int root){queue<int> q;fa[root][0]=root;dep[root]=0;dis[root]=0;q.push(root);while(!q.empty()){int u=q.front();q.pop();for(int i=1;i<20;i++)fa[u][i]=fa[fa[u][i-1]][i-1];for(int i=head[u];i!=-1;i=edge[i].next){int v=edge[i].to;if(v==fa[u][0])continue;dep[v]=dep[u]+1;dis[v]=dis[u]+edge[i].val;fa[v][0]=u;q.push(v);}}}int lca(int x,int y){if(dep[x]<dep[y])swap(x,y);for(int i=0;i<20;i++)if((dep[x]-dep[y])&(1<<i))x=fa[x][i];if(x==y)return x;for(int i=19;i>=0;i--)if(fa[x][i]!=fa[y][i])x=fa[x][i],y=fa[y][i];return fa[x][0];}int main(){     //freopen("data.in","r",stdin);     //freopen("data.out","w",stdout);     int T,n,m; scanf("%d",&T); while(T--){ scanf("%d%d",&n,&m); memset(head,-1,sizeof(head));tol=0; for(int i=1;i<n;i++){ int u,v,w; scanf("%d%d%d",&u,&v,&w); addedge(u,v,w); addedge(v,u,w); } bfs(1); while(m--){ int u,v; scanf("%d%d",&u,&v); printf("%d\n",dis[u]+dis[v]-2*dis[lca(u,v)]); } }     return 0;}