hihoCoder 1515 分数调查（带权并查集）

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 const int maxn = 100000+5;
 5 
 6 int n,m,q;
 7 int p[maxn],r[maxn];
 8 
 9 int finds(int x)
10 {
11     if(p[x]==x)  return x;
12     int tmp = p[x];
13     p[x] = finds(p[x]);
14     r[x] = r[x] + r[tmp];
15     return p[x];
16 }
17 
18 void unions(int a, int b, int x, int y, int s)
19 {
20     p[x] = y;
21     r[x] = s+r[b]-r[a];
22 }
23 
24 int main()
25 {
26     //freopen("in.txt","r",stdin);
27     scanf("%d%d%d",&n,&m,&q);
28     for(int i=1;i<=n;i++)   {p[i]=i;r[i]=0;}
29     while(m--)
30     {
31         int a,b,s;
32         scanf("%d%d%d",&a,&b,&s);
33         int x = finds(a);
34         int y = finds(b);
35         unions(a,b,x,y,s);
36     }
37     while(q--)
38     {
39         int a,b;
40         scanf("%d%d",&a,&b);
41         int x = finds(a);
42         int y = finds(b);
43         if(x!=y)  puts("-1");
44         else printf("%d\n",r[a]-r[b]);
45     }
46     return 0;
47 }