【Loj116】有源汇有上下界最大流（网络流）

题面

Loj

题解

模板题。

#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<cstring>

#include<cmath>

#include<algorithm>

#include<set>

#include<map>

#include<vector>

#include<queue>

using namespace std;

#define ll long long

#define RG register

#define inf 1e9

#define MAX 500

#define MAXL 50000

inline int read()

{

    RG int x=0,t=1;RG char ch=getchar();

    while((ch<'0'||ch>'9')&&ch!='-')ch=getchar();

    if(ch=='-')t=-1,ch=getchar();

    while(ch<='9'&&ch>='0')x=x*10+ch-48,ch=getchar();

    return x*t;

}

struct Line{int v,next,w;}e[MAXL];

int h[MAX],cnt=2;

inline void Add(int u,int v,int w)

{

	e[cnt]=(Line){v,h[u],w};h[u]=cnt++;

	e[cnt]=(Line){u,h[v],0};h[v]=cnt++;

}

int level[MAX],cur[MAX];

bool bfs(int S,int T)

{

	memset(level,0,sizeof(level));level[S]=1;

	queue<int> Q;Q.push(S);

	while(!Q.empty())

	{

		int u=Q.front();Q.pop();

		for(int i=h[u];i;i=e[i].next)

			if(e[i].w&&!level[e[i].v])

				level[e[i].v]=level[u]+1,Q.push(e[i].v);

	}

	return level[T];

}

int dfs(int u,int T,int flow)

{

	if(u==T||!flow)return flow;

	int ret=0;

	for(int &i=cur[u];i;i=e[i].next)

	{

		int v=e[i].v,d;

		if(e[i].w&&level[v]==level[u]+1)

		{

			d=dfs(v,T,min(flow,e[i].w));

			ret+=d;flow-=d;

			e[i].w-=d;e[i^1].w+=d;

			if(!flow)break;

		}

	}

	return ret;

}

int Dinic(int S,int T)

{

	int ret=0;

	while(bfs(S,T))

	{

		memcpy(cur,h,sizeof(cur));

		ret+=dfs(S,T,inf);

	}

	return ret;

}

void Fail(){puts("please go home to sleep");}

int n,m,S,T,SS,TT,M[MAX],ans,rb;

int main()

{

	n=read();m=read();S=read();T=read();

	SS=0;TT=n+1;

	for(int i=1;i<=m;++i)

	{

		int u=read(),v=read(),B=read(),C=read();

		Add(u,v,C-B);M[u]-=B;M[v]+=B;

	}

	for(int i=1;i<=n;++i)

		if(M[i]>=0)Add(SS,i,M[i]);

		else Add(i,TT,-M[i]);

	Add(T,S,inf);rb=cnt-1;Dinic(SS,TT);

	for(int i=h[SS];i;i=e[i].next)if(e[i].w){Fail();return 0;}

	h[T]=e[h[T]].next;h[S]=e[h[S]].next;

	ans+=Dinic(S,T);ans+=e[rb].w;

	printf("%d\n",ans);

	return 0;

}