费用流

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//费用流#include <cstdio>#include <iostream>#include <cstring>using namespace std;const int MAXN = 20000 + 5;const int INF = 0x7f7f7f7f;int from[MAXN<<1],to[MAXN<<1],next[MAXN<<1],cap[MAXN<<1],cos[MAXN<<1];int a[MAXN],q[MAXN],p[MAXN],d[MAXN],fst[MAXN],inq[MAXN];int ecnt=1;inline void add(int f,int t,int c,int cc){    from[++ecnt]=f;    to[ecnt]=t;    cap[ecnt]=c;    cos[ecnt]=cc;        next[ecnt]=fst[f];    fst[f]=ecnt;}int main(){int s,t,n,m;    scanf("%d%d",&m,&n);    s=1;t=n;    for(int i=1;i<=m;i++)    {    int a,b,c,d;     scanf("%d%d%d%d",&a,&b,&c,&d);    add(a,b,c,d);    add(b,a,0,-d);    }    int flow=0,cost=0;while(true){memset(d,0x7f,sizeof(d));memset(inq,0,sizeof(inq));d[s]=0;inq[s]=1;p[s]=0;a[s]=INF;int head=0,tail=0,cnt=0;q[tail++]=s;while(head<tail){if(cnt>m)break;//minus circleint u=q[head++];inq[u]=0;for(int i=fst[u]; i; i=next[i]){if(cap[i]>0 && d[to[i]]>d[u]+cos[i]){d[to[i]]=d[u]+cos[i];p[to[i]]=i;a[to[i]]=min(a[u],cap[i]);if(!inq[to[i]]){q[tail++]=to[i];inq[to[i]]=1;}}}cnt++;}if(d[t]>=INF)break;flow+=a[t];cost+=d[t]*a[t];for(int u=t;u!=s;u=from[p[u]]){cap[p[u]]-=a[t];cap[p[u]^1]+=a[t];}}    printf("%d\n",cost);    return 0;}
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