poj1679最小生成树是否唯一

http://www.cnblogs.com/kuangbin/p/3147329.html  

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N=110;
const int INF=0x3f3f3f3f;
bool vis[N];
int lowc[N],pre[N],Max[N][N];
bool used[N][N];
int Prim(int cost[][N],int n){
     int ans=0;
     memset(vis,0,sizeof(vis));
     memset(Max,0,sizeof(Max));
     memset(used,0,sizeof(used));
     vis[0]=1;
     pre[0]=-1;
     for(int i=1;i<n;++i) {
        lowc[i]=cost[0][i];
        pre[i]=0;
     }
     lowc[0]=0;
     for(int i=1;i<n;++i){
        int minc=INF;
        int p=-1;
        for(int j=0;j<n;++j) if(!vis[j]&&minc>lowc[j]) {
            minc=lowc[j];
            p=j;
        }
        if(minc==INF) return -1;
        ans+=minc;
        vis[p]=1;
        used[p][pre[p]]=used[pre[p]][p]=1;
        for(int j=0;j<n;++j){
            if(vis[j]) Max[j][p]=max(Max[j][pre[p]],lowc[p]);
            if(!vis[j]&&lowc[j]>cost[p][j]) {
                lowc[j]=cost[p][j];
                pre[j]=p;
            }
        }
     }
     return ans;
}
int ans;
int smst(int cost[][N],int n){
    int minn=INF;
    for(int i=0;i<n;++i)
        for(int j=i+1;j<n;++j)
        if(cost[i][j]!=INF&&!used[i][j])
        minn=min(minn,ans+cost[i][j]-Max[i][j]);
    if(minn==INF) return -1;
    return minn;
}
int cost[N][N];
int main(){
    int T,n,m;
    for(scanf("%d",&T);T--;){
        scanf("%d%d",&n,&m);
        int u,v,w;
        for(int i=0;i<n;++i)
            for(int j=0;j<n;++j)
            if(i==j) cost[i][j]=0;
        else cost[i][j]=INF;
        while(m--){
        scanf("%d%d%d",&u,&v,&w);
        --u;--v;
        cost[u][v]=cost[v][u]=w;
        }
        ans=Prim(cost,n);
        if(ans==-1) {
            puts("Not Unique");
            continue;
        }
        if(ans==smst(cost,n)) puts("Not Unique");
        else printf("%d\n",ans);
    }
}