[网络流24题] 餐巾计划

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>

using namespace std;

#define N 4005
#define M 12001

const int inf=1e17;

typedef long long LL;

int tot=1;
int front[N],to[M<<1],nxt[M<<1],from[M<<1];
int cap[M<<1];

int val[M<<1];

int src,decc;

LL cost;

bool vis[N];
LL dis[N];

void read(int &x)
{
    x=0; char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) { x=x*10+c-‘0‘; c=getchar(); }
}

void add(int u,int v,int w,int f)
{
    to[++tot]=v; nxt[tot]=front[u]; front[u]=tot; from[tot]=u; cap[tot]=w; val[tot]=f;
    to[++tot]=u; nxt[tot]=front[v]; front[v]=tot; from[tot]=v; cap[tot]=0; val[tot]=-f;
}

int augment(int now,int flow)
{
    vis[now]=true;
    if(now==decc) 
    {
        cost-=dis[src]*flow;
        return flow;
    }
    int delta;
    for(int i=front[now];i;i=nxt[i])
    {
        if(cap[i] && !vis[to[i]] && dis[to[i]]==dis[now]+val[i])
        {
            delta=augment(to[i],min(flow,cap[i]));
            if(delta)
            {
                cap[i]-=delta;
                cap[i^1]+=delta;
                return delta;
            }
        }
    }
    return 0;
}

bool retreat()
{
    if(vis[decc]) return true;
    LL mi=inf;
    for(int i=2;i<=tot;++i)
        if(cap[i] && vis[from[i]] && !vis[to[i]]) 
            mi=min(mi,dis[from[i]]+val[i]-dis[to[i]]);
    if(mi==inf) return false;
    for(int i=src;i<=decc;++i)
        if(vis[i]) dis[i]-=mi;
    return true;
}

void zkw()
{
    do
    {
        memset(vis,false,sizeof(vis));
        augment(src,inf);
    }while(retreat());
    cout<<cost;
}

int main()
{
    freopen("napkin.in","r",stdin);
    freopen("napkin.out","w",stdout);
    int n,x;
    read(n);
    decc=n*2+1;
    for(int i=1;i<=n;++i)
    {
        read(x);
        add(src,i,x,0);
        add(i+n,decc,x,0);
    }
    for(int i=1;i<n;++i) add(i,i+1,inf,0);
    int p;
    read(p); 
    for(int i=1;i<=n;++i) add(src,i+n,inf,p);
    int a,b;
    read(a); read(b);
    for(int i=1;i+a<=n;++i) add(i,i+a+n,inf,b);
    read(a); read(b);
    for(int i=1;i+a<=n;++i) add(i,i+a+n,inf,b);
    zkw();
}