BZOJ-2768: [JLOI2010]冠军调查（超级裸的最小割）

/**************************************************************
    Problem: 2768
    User: winmt
    Language: C++
    Result: Accepted
    Time:32 ms
    Memory:3064 kb
****************************************************************/
 
#include<iostream>
#include<fstream>
#include<cstdio>
#include<algorithm>
#include<string>
#include<vector>
#include<queue>
#include<deque>
#include<utility>
#include<map>
#include<set>
#include<cmath>
#include<cstdlib>
#include<ctime>
#include<functional>
#include<sstream>
#include<cstring>
#include<bitset>
#include<stack>
using namespace std;
 
int n,m,s,t,cnt=1,x,y,z;
struct sdt
{
    int cap,flow,u,v;
}e[90305];
int nxt[90305],fir[305],d[305],par[305],num[305],cur[305];
bool vis[305];
 
int read()
{
    int x=0;char c=getchar();
    while(c<48||c>57)c=getchar();
    while(c>47&&c<58)x*=10,x+=c-48,c=getchar();
    return x;
}
 
void add(int u,int v,int cp,int fl)
{
    e[++cnt].u=u;e[cnt].v=v;e[cnt].cap=cp;e[cnt].flow=fl;
    nxt[cnt]=fir[u];fir[u]=cnt;
}
 
void bfs()
{
    //memset(vis,0,sizeof(vis));
    //memset(d,0,sizeof(d));
    queue<int>q;
    d[t]=0;
    vis[t]=1;
    q.push(t);
    while(!q.empty())
    {
        int k=q.front();
        q.pop();
        for(int i=fir[k];i;i=nxt[i])
        {
            if(!vis[e[i].v] && e[i].cap==0)
            {
                vis[e[i].v]=1;
                d[e[i].v]=d[k]+1;
                q.push(e[i].v);
            }
        }
    }
}
 
int agument()
{
    int p=t;
    int ans=2147483647;
    while(p!=s)
    {
        ans=min(ans,e[par[p]].cap-e[par[p]].flow);
        p=e[par[p]].u;
    }
    p=t;
    while(p!=s)
    {
        e[par[p]].flow+=ans;
        e[par[p]^1].flow-=ans;
        p=e[par[p]].u;
    }
    return ans;
}
 
int isap()
{
    //memset(num,0,sizeof(num));
    int flow=0;
    for(int i=1;i<=t;i++)
    {
        num[d[i]]++;
        cur[i]=fir[i];
    }
    int p=s;
    while(d[s]<t)
    {
        if(p==t)
        {
            flow+=agument();
            p=s;
        }
        bool ok=0;
        for(int i=cur[p];i;i=nxt[i])
        {
            if(e[i].cap>e[i].flow && d[p]==d[e[i].v]+1)
            {  
                ok=1;  
                par[e[i].v]=i;  
                cur[p]=i;  
                p=e[i].v;  
                break;  
            }  
        }
        if(!ok)
        {
            int mn=t-1;
            for(int i=fir[p];i;i=nxt[i])
            {
                if(e[i].cap>e[i].flow)mn=min(mn,d[e[i].v]);
            }
            if(--num[d[p]]==0)break;
            num[d[p]=mn+1]++;
            cur[p]=fir[p];
            if(p!=s)p=e[par[p]].u;
        }
    }
    return flow;
}
 
int main()
{
    n=read();m=read();
    //memset(nxt,0,sizeof(nxt));
    //memset(fir,0,sizeof(fir));
    s=1;
    t=n+2;
    for(int i=1;i<=n;i++)
    {
        z=read();
        if(z)
        {
            add(s,i+1,1,0);
            add(i+1,s,0,0);
        }
        else
        {
            add(i+1,t,1,0);
            add(t,i+1,1,0);
        }
    }
    for(int i=1;i<=m;i++)
    {
        x=read();y=read();
        add(1+x,1+y,1,0);
        add(y+1,x+1,1,0);
    }
    bfs();
    printf("%d\n",isap());
    return 0;
}