【网络流24题】【COGS14】飞行员搭配问题

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#define MAXN 21050
#define MAXINT 2100000000
using namespace std;
struct edge
{
	int f,c,v;
	edge *next,*rev;
	edge(){};
	edge(int ver,int cap,edge *nex):v(ver),c(cap),f(0),next(nex),rev(NULL){};
	void* operator new(size_t,void *p)
	{
		return p;
	}
}*s[MAXN];
int dis[MAXN],num[MAXN];
int n,m;
int src,des;
int u[10001],v[10001],w[10001];
int un;
int a[10001],b[10001];
int nu;
void init()
{
	int queue[MAXN],head=0,tail=0;
	for (int i=0;i<=des;i++)
	    dis[i]=MAXN,num[i]=0;
	queue[tail++]=des;
	dis[des]=0;
	num[0]=1;
	while (head!=tail)
	{
		int v=queue[head++];
		for (edge *e=s[v];e;e=e->next)
		{
			if ((e->rev&&e->rev->c==0)||dis[e->v]<MAXN) continue;
			dis[e->v]=dis[v]+1;
			++num[dis[e->v]];
			queue[tail++]=e->v;
		}
	}
}
int maxflow()
{
	int st=src,ret=0;
	edge *E[MAXN],*rep[MAXN];
	for (int i=0;i<=n+1;i++) E[i]=s[i];
	while (dis[src]<des)
	{
		if (st==des)
		{
			int delta=MAXINT;
 			for (int i=src;i!=des;i=E[i]->v)
			    delta=min(delta,E[i]->c);
			for (int i=src;i!=des;i=E[i]->v)
			{
				E[i]->c-=delta;
				E[i]->rev->c+=delta;
				E[i]->f+=delta;
				E[i]->rev->f-=delta;
			}
			ret+=delta;
			st=src;
		}
		edge *e;
		for (e=E[st];e;e=e->next)
		    if (e->c>0&&dis[st]==dis[e->v]+1) break;
		if (e)
		{
			E[st]=e;
			rep[e->v]=e->rev;
			st=e->v;
		}
		else
		{
			if ((--num[dis[st]])==0) break;
			E[st]=s[st];    
			int mind=n;
			for (edge *t=s[st];t;t=t->next)
			    if (t->c>0)
			        mind=min(mind,dis[t->v]);
			dis[st]=mind+1;
			++num[dis[st]];
			if (st!=src) st=rep[st]->v;
		}
	}
	return ret;
}
int main()
{
	freopen("flyer.in","r",stdin);
	freopen("flyer.out","w",stdout);
	scanf("%d%d",&n,&m);
	src=0,des=n+1;
	while (~scanf("%d%d",&u[un],&v[un]))w[un++]=1;
	u[un]=0;v[un]=0;
	for (int i=1;i<=m;i++)
	    u[un]=0,v[un]=i,w[un++]=1;
	for (int i=m+1;i<=n;i++)
	    u[un]=i,v[un]=n+1,w[un++]=1;
	edge *buffer=new edge[un*2];
	edge *data=buffer;
	for (int i=0;i<un;i++)
	{
		s[u[i]]=new((void*) data++)edge(v[i],w[i],s[u[i]]);
		s[v[i]]=new((void*) data++)edge(u[i],0,s[v[i]]);
		s[u[i]]->rev=s[v[i]];
		s[v[i]]->rev=s[u[i]];
	}
	init();
	printf("%d",maxflow());
	
}