最小树形图模板

RT，模板题源自洛谷

#include <cstdio>
#include <cstring>
#include <algorithm>
#define N1 105
#define M1 10050
using namespace std;
const int inf=0x3f3f3f3f;

template <typename _T> void read(_T &ret)
{
    ret=0; _T fh=1; char c=getchar();
    while(c<'0'||c>'9'){ if(c=='-') fh=-1; c=getchar(); }
    while(c>='0'&&c<='9'){ ret=ret*10+c-'0'; c=getchar(); }
    ret=ret*fh;
}

struct Edge{
int u[M1],v[M1],w[M1],cte;
void ae(int U,int V,int W)
{ cte++; u[cte]=U; v[cte]=V; w[cte]=W; }
}e;

int n,m,root;
int ine[N1],pre[N1],vis[N1],id[N1];

int zhuliu()
{
    int i,j,x,v,w,cnt,ans=0;
    while(1){
    
    memset(ine,0x3f,sizeof(ine));
    for(j=1;j<=m;j++)
    {
        x=e.u[j]; v=e.v[j];
        if(x!=v && ine[v]>e.w[j])
            ine[v]=e.w[j], pre[v]=x;
    }
    for(i=1;i<=n;i++) if(i!=root && ine[i]==inf)
        return -1;
    memset(vis,0,sizeof(vis)); 
    memset(id,0,sizeof(id)); 
    cnt=0;
    for(i=1;i<=n;i++)
    {
        if(i==root) continue;
        ans+=ine[i];
        x=i;
        while(vis[x]!=i && !id[x] && x!=root)
        {
            vis[x]=i; x=pre[x];
        }
        if(!id[x] && x!=root)
        {
            id[x]=++cnt;
            for(v=pre[x];v!=x;v=pre[v]) id[v]=cnt;
        }
    }
    if(!cnt) break; 
    for(i=1;i<=n;i++) if(!id[i])
        id[i]=++cnt;
    for(i=1;i<=m;i++)
    {
        if(id[e.u[i]]!=id[e.v[i]]) e.w[i]-=ine[e.v[i]];
        e.u[i]=id[e.u[i]]; e.v[i]=id[e.v[i]];
    }
    n=cnt;
    root=id[root];
    
    }
    return ans;
}

int main()
{
    int i,j,x,y,w,ans;
    scanf("%d%d%d",&n,&m,&root);
    for(i=1;i<=m;i++) read(x), read(y), read(w), e.ae(x,y,w);
    ans=zhuliu();
    printf("%d
",ans);
    return 0;    
}