UVA 10462 Is There A Second Way Left? 次小生成树

模板题

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <cmath>
#include <vector>
using namespace std;
const int N=105;
const int INF=0x3f3f3f3f;
int fa[N],head[N],tot,T,n,m,d[N][N];
struct Edge{
    int v,next,w;
}edge[N<<1];
void add(int u,int v,int w){ 
   edge[tot].v=v;
   edge[tot].w=w;
   edge[tot].next=head[u];
   head[u]=tot++;
}
struct Node{
  int u,v,w;
  bool mark;
  bool operator<(const Node &rhs)const{
      return w<rhs.w;
  }
}p[N<<1];
int find(int x){
    return x==fa[x]?x:fa[x]=find(fa[x]);
}
int s;
void dfs(int u,int f,int t){
   d[s][u]=t;
   for(int i=head[u];~i;i=edge[i].next){
        int v=edge[i].v;
        if(v==f)continue;
        dfs(v,u,max(t,edge[i].w));
   }
}
int main()
{
    int cas=0;
    scanf("%d",&T);
    while(T--){
        scanf("%d%d",&n,&m);
        tot=0;
        printf("Case #%d : ",++cas);
        memset(d,0,sizeof(d));
        for(int i=1;i<=n;++i)fa[i]=i,head[i]=-1;
        for(int i=1;i<=m;++i){
          scanf("%d%d%d",&p[i].u,&p[i].v,&p[i].w);
          p[i].mark=0;
        }
        sort(p+1,p+1+m);
        int tmp=n;
        int mst=0,ans=INF;
        for(int i=1;i<=m;++i){
            int u=find(p[i].u),v=find(p[i].v);
            if(u!=v){
              --tmp;
              fa[u]=v;
              mst+=p[i].w;
              p[i].mark=1;
              add(p[i].u,p[i].v,p[i].w);
              add(p[i].v,p[i].u,p[i].w);
              if(tmp==1)break;
            }
        }
        if(tmp>1){
           printf("No way\n");
           continue;
        }
        for(int i=1;i<=n;++i){
            s=i;dfs(i,0,0);
        }
        for(int i=1;i<=m;++i){
         if(p[i].mark)continue;
         ans=min(ans,mst-d[p[i].u][p[i].v]+p[i].w);
        }
        if(ans==INF)printf("No second way\n");
        else printf("%d\n",ans);
    }
    return 0;
}