题目链接：

！a b w 表示b比a大w

?  a b  输出b比a大多少

#include
     
      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"<