zkw费用流模板

Posted 2020-10-18 日拱一卒 功不唐捐

 

理论：http://www.cnblogs.com/acha/p/6735037.html

 

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

using namespace std;

#define N 5001
#define M 50001

const int inf=1e9;

int n,m,src,decc;

int tot=1;

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

int max_flow,cost;

int dis[N];
bool vis[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; val[tot]=f; cap[tot]=w;
    to[++tot]=u; nxt[tot]=front[v]; front[v]=tot; from[tot]=v; val[tot]=-f; cap[tot]=0;
}

int augment(int now,int flow)
{
    vis[now]=true;
    if(now==decc)
    {
        cost+=-dis[src]*flow;
        max_flow+=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;
    int 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=1;i<=n;++i)
        if(vis[i]) dis[i]-=mi;
    return true;
}

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

int main()
{
    read(n); read(m); read(src); read(decc);
    int u,v,w,f;
    while(m--)
    {
        read(u); read(v); read(w);read(f);
        add(u,v,w,f);
    }
    zkw();
}