HDOJ 2586 How far away? LCA

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<algorithm>
 4 #include<vector>
 5 using namespace std;
 6 
 7 typedef pair<int, int> P;
 8 const int maxn = 40100;
 9 
10 int T, n, m, x, y, z;
11 int f[maxn], d[maxn], ans[300];
12 bool vis[maxn];
13 vector<P> e[maxn], q[maxn];
14 
15 int getf(int x)
16 {
17     if (f[x] == x) return x;
18     return f[x] = getf(f[x]);
19 }
20 void unionxy(int x, int y)
21 {
22     int xroot = getf(x), yroot = getf(y);
23     f[yroot] = xroot;
24 }
25 void tarjan(int x)
26 {
27     f[x] = x;
28     vis[x] = true;
29     for (int i = 0; i < q[x].size(); i++){
30         int v = q[x][i].first, id = q[x][i].second;
31         if (vis[v]){
32             int lca = f[getf(v)];
33             ans[id] = d[x] + d[v] - 2 * d[lca];
34         }
35     }
36     for (int i = 0; i < e[x].size(); i++){
37         int v = e[x][i].first, w = e[x][i].second;
38         if (!vis[v]){
39             d[v] = d[x] + w;
40             tarjan(v);
41             unionxy(x, v);
42             f[getf(x)] = x;
43         }
44     }
45 }
46 int main()
47 {
48     scanf("%d", &T);
49     while(T--)
50     {
51         scanf("%d %d", &n, &m);
52         for (int i = 0; i <= n; i++){
53             q[i].clear(); e[i].clear();
54         }
55         for (int i = 1; i < n; i++){
56             scanf("%d%d%d", &x, &y, &z);
57             e[x].push_back(make_pair(y, z));
58             e[y].push_back(make_pair(x, z));
59         }
60         for (int i = 0; i < m; i++){
61             scanf("%d %d", &x, &y);
62             if (x == y) ans[i] = 0;
63             else{
64                 q[x].push_back(make_pair(y, i));
65                 q[y].push_back(make_pair(x, i));
66             }
67         }
68         memset(vis, 0, sizeof(vis));
69         d[1] = 0;
70         tarjan(1);
71         for (int i = 0; i < m; i++)
72             printf("%d\n", ans[i]);
73     }
74     return 0;
75 }