2012东北地区赛C题(缩点+bfs)

数据出水了，直接bfs也能过。

下面是我写的缩点+bfs的方法。

/*
Source Code
Problem: 1003
Username: 2010201211
Run Time: 36MS
Memory: 5188K
Language:C++
JudgeStatus: Accepted
*/
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <algorithm>
using namespace std;
#define V 1005
#define E 1005000
int n,m,dfn[V],low[V];
int top,cnt,indexs,ecnt;
bool instack[V];
int stack[V],id[V],num[V],in[V],out[V],w[V],vis[V],queue[V],sum[V];
int map[V][V];
int head[V];
struct edge{
    int s,t,cost,next;
}e[E];
void addedge(int u,int v){
    e[ecnt].s=u;
    e[ecnt].t=v;
    e[ecnt].next=head[u];
    head[u]=ecnt++;
}
void tarjan(int u){
    int v;
    int tmp;
    dfn[u]=low[u]=++indexs;
    instack[u]=true;
    stack[++top]=u;
    for(int k=head[u];k!=-1;k=e[k].next){
        v=e[k].t;
        if(!dfn[v]){
            tarjan(v);
            if(low[v]<low[u])
                low[u]=low[v];
        }
        else if(instack[v] && dfn[v]<low[u]){
            low[u]=dfn[v];
        }
    }
    if(dfn[u]==low[u]){
        cnt++;
        do{
            tmp=stack[top--];
            instack[tmp]=false;
            id[tmp]=cnt;
            num[cnt]+=w[tmp];
        }
        while(tmp!=u);
    }
}
void suodian(){

    for(int i=1;i<=n;i++){
        int tmp=id[i];
        for(int k=head[i];k!=-1;k=e[k].next){
            int tmp1=id[e[k].t];
            if(id[i]!=id[e[k].t]){
                out[tmp]++;
                in[tmp1]++;
                map[tmp][tmp1]=1;
            }
        }
    }
    /*cout <<"id:";
    for(int i=1;i<=n;i++){
        printf("%d ",id[i]);
    }
    cout << endl<<"in:";
    for(int i=1;i<=cnt;i++){
        printf("%d ",in[i]);
    }
    cout << endl<<"out:";
    for(int i=1;i<=cnt;i++){
        printf("%d ",out[i]);
    }
    cout << endl<<"num:";
    for(int i=1;i<=cnt;i++){
        printf("%d ",num[i]);
    }
    cout << endl;*/
}
void bfs(int u){
    memset(vis,0,sizeof(vis));
    vis[u]=1;
    int v,head=0,tail=0;
    sum[u]+=num[u];
   // cout << sum[u] << endl;
    queue[tail++]=u;
    while(head<tail){
        v=queue[head++];
        for(int i=1;i<=cnt;i++){
            if(map[i][v]==1 && vis[i]==0){
                vis[i]=1;
                sum[u]+=num[i];
                //cout << sum[u] << endl;
                queue[tail++]=i;
            }
        }
    }
}
void findmax(){
    int mmax=-1;
    int mmin=1050;
    for(int i=1;i<=cnt;i++){
        if(out[i]==0){
            bfs(i);
            if(sum[i]>mmax){
                mmax=sum[i];
                /*for(int j=1;j<=n;j++){
                    if(id[j]==i && j<mmin){
                        mmin=j;
                    }
                }*/
            }
        }
    }
    for(int i=1;i<=cnt;i++){
        if(out[i]==0){
            if(sum[i]==mmax){
                for(int j=1;j<=n;j++){
                    if(id[j]==i && j<mmin){
                        mmin=j;
                    }
                }
            }
        }
    }
    /*for(int i=1;i<=cnt;i++){
        printf("%d ",sum[i]);
    }
    cout << endl;*/
    printf("%d\n",mmin);
}
void solve(){

    top=cnt=indexs=0;
    memset(dfn,0,sizeof(dfn));
    memset(num,0,sizeof(num));
    memset(sum,0,sizeof(sum));
    memset(map,0,sizeof(map));
    memset(id,0,sizeof(id));
    memset(in,0,sizeof(in));
    memset(out,0,sizeof(out));
    for(int i=1;i<=n;i++){
        if(!dfn[i])
            tarjan(i);

    }
    suodian();
    findmax();
}
int main()
{
    //freopen("in.txt","r",stdin);
    int a,b;
    while(scanf("%d%d",&n,&m)!=EOF){
        for(int i=1;i<=n;i++){
            scanf("%d",&w[i]);
        }
        ecnt=0;
        memset(head,-1,sizeof(head));
        for(int i=1;i<=m;i++){
            scanf("%d%d",&a,&b);
            addedge(b,a);
        }
        solve();
    }
    return 0;
}