【tarjan缩点】hdu 3072

这题要先缩点在找没有入边的点，再找权值最小的边，注意：可能有重边，看sample3就知道！

用vector和stack的缘故，比较慢500+ms

#include <list>
#include <map>
#include <set>
#include <queue>
#include <string>
#include <deque>
#include <stack>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <math.h>
#include <cstdlib>
#include <limits.h>
#include <time.h>
#include <string.h>
using namespace std;
#define LL long long
#define PI acos(-1.0)
#define FRE freopen("a.txt","r",stdin)
#define MAX INT_MAX
#define MIN INT_MIN
#define eps 1e-10
#define MOD 1000000007
#define N  50005
int min(int a,int b){return a<b?a:b;}
struct node{
    int t;
    int w;
};
int n,m;
vector<node> v[N];
stack<int> s;
bool vis[N];
bool Instack[N];
int low[N],dfn[N];
int belong[N];
int step,t;
int cost[N];
void init(){
    int i;
    for(i=0;i<=n;i++){
        v[i].clear();
        vis[i]=0;
        low[i]=dfn[i]=0;
        Instack[i]=0;
        belong[i]=0;
        cost[i]=MAX;
    }
    while(!s.empty())s.pop();
    t=0;
    step=0;
}
void tarjan(int u){
    vis[u]=1;
    step++;
    s.push(u);
    Instack[u]=1;
    low[u]=dfn[u]=step;
    int i,j;
    for(i=0;i<v[u].size();i++){
        int x=v[u][i].t;
        if(!vis[x]){
            tarjan(x);
            low[u]=min(low[u],low[x]);
        }
        else{
            if(Instack[x])
            low[u]=min(low[u],dfn[x]);
        }
    }
    if(low[u]==dfn[u]){
        t++;
        while(1){
            int x=s.top();
            s.pop();
            belong[x]=t; ////
            Instack[x]=0;
            if(x==u)break;
        }
    }
}
void gao(){
    int i,j;
    for(i=0;i<n;i++)
    if(!vis[i])
    tarjan(i);
    for(i=0;i<n;i++){
        int x=belong[i];
        for(j=0;j<v[i].size();j++){
            int y=belong[v[i][j].t];
            if(x==y)continue;
            else{
                cost[y]=min(cost[y],v[i][j].w);
            }
        }
    }
    int ans=0;
    for(i=0;i<n;i++){
        if(cost[i]!=MAX)
        ans+=cost[i];
    }
    printf("%d\n",ans);
}
int main(){
    while(scanf("%d%d",&n,&m)!=EOF){
        int i,j;
        init();
        while(m--){
            int a,b,c;
            scanf("%d%d%d",&a,&b,&c);
            node tmp;
            tmp.t=b;
            tmp.w=c;
            v[a].push_back(tmp);
        }
        gao();
    }
    return 0;
}