【tarjan缩点】hdu 3072

来源：互联网发布：php加密代码编辑：程序博客网时间：2024/06/07 14:18
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  50005int 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;}