hihocoder1515：带权并查集

题解：带权并查集

建议大家先学习一下HDU3038，其它的都一样。代码如下

#include <bits/stdc++.h>
using namespace std;
int const N = 100000 + 10;
int n,m,q,fa[N],val[N];
void Init(){
	for(int i=0;i<=n;i++)	fa[i] = i,val[i] = 0;
}
int find(int x){
	if(x != fa[x]){
		int t = fa[x];
		fa[x] = find(fa[x]);
		val[x] += val[t];
	}
	return fa[x];
}
int main(){
	ios::sync_with_stdio(false);
	cin>>n>>m>>q;
	int x,y,s;
	Init();
	for(int i=1;i<=m;i++){
		cin>>x>>y>>s;
		int px = find(x),	py = find(y);
		if(px != py){
			fa[px] = py;
			val[px] = s + val[y] - val[x];
		}
	}
	for(int i=1;i<=q;i++){
		cin>>x>>y;
		int px = find(x),	py = find(y);
		if(px != py)	cout<<-1<<endl;
		else cout<<val[x] - val[y]<<endl;
	}
	return 0;

}