POJ1986 Distance Queries (LCA)

 1 #include<set>
 2 #include<queue>
 3 #include<cstdio>
 4 #include<cstdlib>
 5 #include<cstring>
 6 #include<iostream>
 7 #include<algorithm>
 8 using namespace std;
 9 const int N = 100010;
10 #define For(i,n) for(int i=1;i<=n;i++)
11 #define Rep(i,l,r) for(int i=l;i<=r;i++)
12 
13 struct Edge{
14     int t,next,w;
15 }E[N*2];
16 vector< pair<int,int> > Q[N];
17 int s,t,w,Es,ans[N],head[N],fa[N],d[N];
18 bool vis[N];
19 
20 int find(int i){
21     if(fa[i]==i) return i;
22     else         return find(fa[i]);
23 }
24 
25 void makelist(int s,int t,int w){
26     E[Es].t = t; E[Es].w = w;E[Es].next = head[s];
27     head[s] = Es++;
28 }
29 
30 void LCA(int i,int w){
31     d[i] = w;fa[i] = i;
32     vis[i] = true;
33     for(int p=head[i];p!=-1;p=E[p].next)
34         if(!vis[E[p].t]){
35             LCA(E[p].t,w+E[p].w);
36             fa[E[p].t] = i;
37         }
38     int  len = Q[i].size();
39     for(int j=0;j<len;j++){
40         if(vis[Q[i][j].first])
41             ans[Q[i][j].second] = w + d[Q[i][j].first] - 2 * d[find(Q[i][j].first)]; 
42     }
43 }
44 int n,m,qn;
45 int main(){
46     memset(head,-1,sizeof(head));
47     scanf("%d%d",&n,&m);
48     For(i,m){
49         scanf("%d%d%d %*c",&s,&t,&w);
50         makelist(s,t,w);makelist(t,s,w);
51     }
52     scanf("%d",&qn);
53     For(i,qn){
54         scanf("%d%d",&s,&t);
55         Q[s].push_back(make_pair(t,i));Q[t].push_back(make_pair(s,i));
56     }
57     LCA(1,0);
58     For(i,qn) printf("%d\n",ans[i]);
59     return 0;
60 }