LCA距离

 1 #include <iostream>
 2 #include <stdio.h>
 3 #include <string.h>
 4 #include <vector>
 5 using namespace std;
 6 const int N = 40010;
 7 struct Nod{
 8     int to, w;
 9     Nod(int a = 0, int b = 0){
10         to = a; w = b;
11     }
12 };
13 int ans[N];
14 int par[N],vis[N],mark[N],dis[N];
15 int n,m;
16 vector<Nod> mp[N];
17 vector<Nod> query[N];
18 void init(){
19     for(int i = 0; i <= n; i ++){
20         mp[i].clear();
21         query[i].clear();
22         vis[i] = mark[i] = 0;
23         par[i] = i;
24     }
25     memset(ans,-1,sizeof(ans));
26 }
27 int findset(int x){
28     if(x != par[x]) par[x] = findset(par[x]);
29     return par[x];
30 }
31 
32 void dfs(int u){
33     for(int i = 0; i < query[u].size(); i ++){
34         int v = query[u][i].to;
35         if(vis[v]&&ans[query[u][i].w]==-1&&!mark[findset(v)]){
36             ans[query[u][i].w] = dis[u]+dis[v]-2*dis[findset(v)];
37         }
38     }
39     for(int i = 0; i < mp[u].size(); i++){
40         int v = mp[u][i].to;
41         if(!vis[v]){
42             vis[v] = 1;
43             dis[v] = dis[u]+mp[u][i].w;
44             dfs(v);
45             par[v] = u;
46         }
47     }
48 }
49 
50 int main(){
51     int t;
52     scanf("%d",&t);
53     while(t--){
54         scanf("%d%d",&n,&m);
55         init();
56         int x, y, z;
57         for(int i = 0; i < n-1; i ++){
58             scanf("%d%d%d",&x,&y,&z);
59             mp[x].push_back(Nod(y,z));
60             mp[y].push_back(Nod(x,z));
61         }
62         for(int i = 1; i <= m; i ++){
63             scanf("%d%d",&x,&y);
64             query[x].push_back(Nod(y,i));
65             query[y].push_back(Nod(x,i));
66         }
67         for(int i = 1; i <= n; i ++){            
68             if(!vis[i]){
69                 printf("%d+++\n",i);
70                 vis[i] = 1;
71                 dis[i] = 0;
72                 dfs(i);
73                 mark[i] = 1;
74             }
75         }
76         for(int i = 1; i <= m; i ++){
77             printf("%d\n",ans[i]);
78         }
79     }
80     return 0;
81 }