bzoj2768: [JLOI2010]冠军调查(双倍经验最小割)

2768: [JLOI2010]冠军调查

题目：传送门

题解：
　　 双倍经验（1934）

代码：

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#define qread(x) x=read()
using namespace std;
inline int read()
{
    int f=,x=;char ch;
    while(ch<'' || ch>''){if(ch=='-')f=-;ch=getchar();}
    while(ch>='' && ch<=''){x=x*+ch-'';ch=getchar();}
    return f*x;
}
struct node
{
    int x,y,c,next,other;
}a[];int len,last[];
int n,m,st,ed;
void ins(int x,int y,int c)
{
    int k1,k2;
    k1=++len;
    a[len].x=x;a[len].y=y;a[len].c=c;
    a[len].next=last[x];last[x]=len;

    k2=++len;
    a[len].x=y;a[len].y=x;a[len].c=;
    a[len].next=last[y];last[y]=len;

    a[k1].other=k2;
    a[k2].other=k1;
}
int list[],h[],head,tail;
bool bt_h()
{
    memset(h,,sizeof(h));h[st]=;
    list[]=st;head=;tail=;
    while(head!=tail)
    {
        int x=list[head];
        for(int k=last[x];k;k=a[k].next)
        {
            int y=a[k].y;
            if(h[y]== && a[k].c>)
            {
                h[y]=h[x]+;
                list[tail++]=y;
            }
        }
        head++;
    }
    if(h[ed]>)return true;
    return false;
}
int find_flow(int x,int flow)
{
    if(x==ed)return flow;
    int s=,t;
    for(int k=last[x];k;k=a[k].next)
    {
        int y=a[k].y;
        if(h[y]==h[x]+ && a[k].c> && s<flow)
        {
            s+=t=find_flow(y,min(a[k].c,flow-s));
            a[k].c-=t;a[a[k].other].c+=t;
        }
    }
    if(s==)h[x]=;
    return s;
}
int main()
{
    qread(n);qread(m);
    len=;memset(last,,sizeof(last));
    st=-;ed=st+;
    for(int i=;i<=n;i++)
    {
        int x;qread(x);
        if(x==)ins(st,i,);
        else ins(i,ed,);
    }
    for(int i=;i<=m;i++)
    {
        int x,y;
        qread(x);qread(y);
        ins(x,y,);
        ins(y,x,);
    }
    int ans=;
    while(bt_h())ans+=find_flow(st,);
    printf("%d\n",ans);
    return ;
}