HDU 3072

#include<stdio.h>
#include<string.h>
#include<stack>
#include<string>
#include<math.h>
#include<queue>
#include<set>
#include<algorithm>
#include<iostream>
#include<vector>
#include<map>
using namespace std;
#define LL long long
#define inf 199999999
#define N 50010
struct node
{
    int v,to,w;
}edge[N<<2];
int low[N],dfn[N],vis[N],belong[N],ans[110],head[N];
stack<int>s;
int cnt,n,m,Index,sum,e;
void init()
{
    memset(low,0,sizeof(low));
    memset(dfn,0,sizeof(dfn));
    memset(vis,0,sizeof(vis));
    memset(belong,0,sizeof(belong));
    memset(head,-1,sizeof(head));
    while(!s.empty()) s.pop();
    Index=cnt=sum=e=0;
}
void tarjan(int u)
{
    low[u]=dfn[u]=++Index;
    s.push(u);vis[u]=1;
    for(int i=head[u];i!=-1;i=edge[i].to)
    {
        int v=edge[i].v;
        if(!dfn[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(vis[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        int v;
        cnt++;
        do
        {
            v=s.top();s.pop();
            belong[v]=cnt;
            vis[v]=0;
        }while(u!=v);
    }
}
int main()
{
    int i,j,u,v,w;
    while(scanf("%d%d",&n,&m)!=-1)
    {
        init();
        for(i=1;i<=m;i++)
        {
            scanf("%d%d%d",&u,&v,&w);
            u++;v++;
            edge[e].v=v;
            edge[e].w=w;
            edge[e].to=head[u];
            head[u]=e++;
        }
        for(i=1;i<=n;i++)
        {
            if(dfn[i]==0)
                tarjan(i);
        }
        memset(ans,127,sizeof(ans));
        for(u=1;u<=n;u++)
        {
            for(i=head[u];i!=-1;i=edge[i].to)
            {
                v=edge[i].v;
                if(belong[u]!=belong[v])
                    ans[belong[v]]=min(ans[belong[v]],edge[i].w);
            }
        }
        for(i=1;i<=cnt;i++) if(ans[i]<inf) sum+=ans[i];
        printf("%d\n",sum);
    }
    return 0;
}