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 ;

}