「网络流 24 题」飞行员配对方案问题

Question

哪儿都有

Solution

匈牙利裸题，但我作死 打了网络流。

Code

#include<cstdio>
#include<algorithm>
#define N 10010
using namespace std;
struct node{int v,fr,c;}e[N<<3];
int n,m,x,y,tail[N<<1],S=0,T,cnt=1,ans=0;
int dis[N<<1],gap[N<<1];

inline int read()
{
	int x=0,f=0; char c=getchar();
	while (c<'0' || c>'9') f=(c=='-') ? 1:f,c=getchar();
	while (c>='0' && c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
	return f ? -x:x;
}

inline void add(int u,int v)
{
	e[++cnt]=(node){v,tail[u],1}; tail[u]=cnt;
	e[++cnt]=(node){u,tail[v],0}; tail[v]=cnt;
}

int dfs(int x,int hav)
{
	if (x==T) return hav;
	int gone=0;
	for (int p=tail[x],v,can;p;p=e[p].fr)
	{
		v=e[p].v;
		if (dis[x]!=dis[v]+1) continue;
		can=dfs(v,min(e[p].c,hav-gone));
		e[p].c-=can;e[p^1].c+=can;gone+=can;
		if (gone==hav) return gone;
	}
	gap[dis[x]]--;
	if (!gap[dis[x]]) dis[1]=T;
	gap[++dis[x]]++;
	return gone;
}

int main()
{
	freopen("air.in","r",stdin);
	freopen("air.out","w",stdout);
	n=read(),m=read();T=m+1;
	x=read(),y=read();
	while (x!=-1) add(x,y),x=read(),y=read();
	for (int i=1;i<=n;i++) add(S,i);
	for (int i=n+1;i<=m;i++) add(i,T);
	while (dis[1]!=T) ans+=dfs(S,1000000);
	if (ans==0) {puts("No Solution!"); return 0;}
	printf("%d
",ans);
	for (int i=1;i<=n;i++)
		for (int p=tail[i];p;p=e[p].fr)
			if (e[p].v>=n+1 && e[p].v<=m && e[p].c==0)
				{printf("%d %d
",i,e[p].v); break;}
	return 0;
}