Never Wait for Weights（带权并查集+路径压缩）

题目链接：http://acm.sdibt.edu.cn/vjudge/contest/view.action?cid=2209#problem/F

！a b w 表示b比a大w

?  a b  输出b比a大多少

#include<iostream>
using namespace std;
const int maxn = 100005;
int fa[maxn],val[maxn];

int find_(int x){
    if(x != fa[x])
    {
        int t=fa[x];
        fa[x]=find_(fa[x]);
        val[x]+=val[t];
        return fa[x];
    }//路径压缩
    return x;
}
void merge_(int a,int b,int c){
    int fx,fy;
    fx=find_(a);
    fy=find_(b);
    if(fx != fy)
    {
        fa[fx]=fy;
        val[fx]=val[b]+c-val[a];
    }
}
int main(){
    int n,m;
    while(cin>>n>>m&&n&&m){
       char t;
       int a,b,c;
       for(int i=1;i<=m;i++)
        fa[i]=i,val[i]=0;
       while(m--){
        cin>>t>>a>>b;
        if(t == '!')
        {
            cin>>c;
            merge_(a,b,c);
        }
        else
        {
            int fx,fy;
            fx=find_(a),fy=find_(b);
            if(fx != fy)
            cout<<"UNKNOWN"<<endl;
            else
            cout<<val[a]-val[b]<<endl;
        }
       }
    }
}