网络流24题 负载平衡 费用流

转化成供求平衡以后直接连就好了。。

#include<cstdio>#include<algorithm>#include<iostream>#include<cstring>#define fo(i,a,b) for(int i=a;i<=b;i++)#define fd(i,a,b) for(int i=a;i>=b;i--)#define T 2001using namespace std;const int inf=0x7fffffff;const int N=2005;int n,m;int head[N],q[N],dis[N],from[N],a[N];int cnt=1,sum,ans;bool vis[N];struct node{    int from,to,next,v,c;}e[100001];inline void add(int u,int v,int w,int c){    cnt++;    e[cnt].from=u;e[cnt].to=v;    e[cnt].v=w;e[cnt].c=c;    e[cnt].next=head[u];head[u]=cnt;}inline void ins(int x,int y,int w,int c){    add(x,y,w,c);    add(y,x,0,-c);}bool spfa(){    for(int i=0;i<=T;i++)dis[i]=inf;    int t=0,w=1,i,now;    dis[0]=q[0]=0;    vis[0]=1;    while(t!=w)    {        now=q[t];t++;if(t==2001)t=0;        for(int i=head[now];i;i=e[i].next)        {            if(e[i].v&&dis[e[i].to]>dis[now]+e[i].c)            {                from[e[i].to]=i;                dis[e[i].to]=dis[now]+e[i].c;                if(!vis[e[i].to])                {                    vis[e[i].to]=1;                    q[w++]=e[i].to;                    if(w==2001)w=0;                }            }        }        vis[now]=0;    }    if(dis[T]==inf)return 0;return 1;}inline void mcf(){    int i,x=inf;    i=from[T];    while (i)    {        x=min(e[i].v,x);        i=from[e[i].from];    }    i=from[T];    while (i)    {        e[i].v-=x;        e[i^1].v+=x;        ans+=x*e[i].c;        i=from[e[i].from];    }}int main(){    scanf("%d",&n);    fo(i,1,n)    {        scanf("%d",&a[i]);        sum+=a[i];    }    sum/=n;    fo(i,1,n)a[i]-=sum;    fo(i,1,n)    {        if (a[i]>0)ins(0,i,a[i],0);        else ins(i+n,T,-a[i],0);    }    fo(i,1,n)    {        if (i!=1)        {            ins(i,i-1,inf,1);            ins(i,i-1+n,inf,1);        }        if (i!=n)        {            ins(i,i+1,inf,1);            ins(i,i+1+n,inf,1);        }    }    ins(n,1,inf,1);    ins(n,n+1,inf,1);    ins(1,n,inf,1);    ins(1,n+n,inf,1);    while (spfa())mcf();    printf("%d\n",ans);}