POJ1815_Friendship

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#define maxn 5555
#define maxm 555555
using namespace std;

int to[maxm],next[maxm],c[maxm],belong[maxm],first[maxm],edge;
int d[maxn],tag[maxn],TAG=222;
bool can[maxn],go[maxn];
int Q[maxn],bot,top;
int f[511][511];
int s,t,n,pos[maxn];

void _init()
{
    edge=-1;
    for (int i=1; i<=n+n; i++) first[i]=-1,go[i]=false;
}

void addedge(int U,int V)
{
    edge++;
    to[edge]=V,c[edge]=1,next[edge]=first[U],first[U]=edge;
    edge++;
    to[edge]=U,c[edge]=0,next[edge]=first[V],first[V]=edge;
}

bool bfs()
{
    Q[bot=top=1]=t,tag[t]=++TAG,d[t]=0,can[t]=false;
    while (bot<=top)
    {
        int cur=Q[bot++];
        for (int i=first[cur]; i!=-1; i=next[i])
            if (c[i^1]>0 && tag[to[i]]!=TAG && !go[to[i]])
            {
                tag[to[i]]=TAG,d[to[i]]=d[cur]+1;
                can[to[i]]=false,Q[++top]=to[i];
                if (to[i]==s) return true;
            }
    }
    return false;
}

int dfs(int cur,int num)
{
    if (cur==t) return num;
    int tmp=num,k;
    for (int i=first[cur]; i!=-1; i=next[i])
        if (c[i]>0 && tag[to[i]]==TAG && d[to[i]]==d[cur]-1 && !can[to[i]])
        {
            k=dfs(to[i],min(num,c[i]));
            if (k) num-=k,c[i]-=k,c[i^1]+=k;
            if (!num) break;
        }
    if (num) can[cur]=true;
    return tmp-num;
}

int maxflow()
{
    int flow=0;
    while (bfs()) flow+=dfs(s,~0U>>1);
    return flow;
}

int get(int x)
{
    for (int i=first[x]; i!=-1; i=next[i])
        if (c[i]==0 && !(i&1))
        {
            int tmp=to[i];
            tmp-=x;
            if (tmp<0) tmp=-tmp;
            if (tmp!=n) return get(to[i]);
            tmp=min(x,to[i]);
            return min(tmp,get(to[i]));
        }
    return ~0U>>1;
}

int main()
{
    int tmp,mf;
    vector<int> ans;
    while (scanf("%d%d%d",&n,&s,&t)!=EOF)
    {
        _init();
        for (int i=1; i<=n; i++) addedge(i,i+n),pos[i]=edge;
        for (int i=1; i<=n; i++)
            for (int j=1; j<=n; j++)
            {
                scanf("%d",&tmp);
                f[i][j]=f[j][i]=tmp;
                if (i>=j) continue;
                if (tmp) addedge(i+n,j),addedge(j+n,i);
            }
        if (s==t || f[s][t])
        {
            puts("NO ANSWER!");
            continue;
        }
        s+=n;
        ans.clear();
        mf=maxflow();
        printf("%d\n",mf);
        if (mf==0) continue;
        for (int i=1; i<=n && mf>0; i++)
        {
            if (i==s-n || i==t) continue;
            for (int j=0; j<edge; j+=2) c[j]+=c[j+1],c[j+1]=0;
            go[i]=true,go[i+n]=true;
            tmp=maxflow();
            if (tmp<mf) ans.push_back(i),mf--;
                else go[i]=false,go[i+n]=false;
        }
        
        sort(ans.begin(),ans.end());
        printf("%d",ans[0]);
        for (unsigned i=1; i<ans.size(); i++) printf(" %d",ans[i]);
        printf("\n"); 
    }
    return 0;
}