【codevs1916】[網絡流24題]負載平衡問題

XJB建建圖就好了，按照差分後的等式建圖，其實完全不用差分自己yy就可以想得到，直接求費用流

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

using namespace std;
const int N=1010;
const int inf=0x3f3f3f3f;
int n,m,te,sz,eva,s,t;
int inq[N],d[N],val[N],a[N],head[N],p[N];
struct edge{
    int u,v,cap,flow,next,cost;
}e[10010];
queue<int>q;

void add(int u,int v,int cap,int cost)
{
    e[++te].u=u;
    e[te].v=v;
    e[te].cap=cap;
    e[te].flow=0;
    e[te].cost=cost;
    e[te].next=head[u];
    head[u]=te;
}
void insert(int u,int v,int cap,int cost){add(u,v,cap,cost);add(v,u,0,-cost);}
int spfa(int &cost,int &flow)
{
    memset(d,0x3f,sizeof(d));
    memset(a,0,sizeof(a));
    q.push(s);d[s]=0;
    inq[s]=1;a[s]=inf;
    while(!q.empty())
    {
        int u=q.front();
        for (int i=head[u];i;i=e[i].next)
        {
            int v=e[i].v;
            if (e[i].cap>e[i].flow&&d[v]>d[u]+e[i].cost)
            {
                p[v]=i;
                a[v]=min(a[u],e[i].cap-e[i].flow);
                d[v]=d[u]+e[i].cost;
                if (!inq[v])
                {
                    q.push(v);
                    inq[v]=1;
                }
            }
        }
        inq[u]=0;
        q.pop();
    }
    if(!a[t])return 0;
    cost+=d[t]*a[t];
    flow+=a[t];
    for (int u=t;u!=s;u=e[p[u]].u)
    {
        e[p[u]].flow+=a[t];
        e[p[u]^1].flow-=a[t];
    }
    return 1;
}
int mcmf(int &cost)
{
    int flow=0;cost=0;
    while(spfa(cost,flow));
    return flow;
}
int main()
{
    te=1;
    cin>>n;
    int tot=0;
    for (int i=1;i<=n;++i)
    scanf("%d",&val[i]),tot+=val[i];
    if (tot%n)return 0;
    tot/=n,s=n+1,t=s+1;
    for (int i=1;i<=n;++i)
    {
        if (val[i]>tot)insert(s,i,val[i]-tot,0);
        else insert(i,t,tot-val[i],0);
        if (i!=1)insert(i,i-1,inf,1);
        if (i!=n)insert(i,i+1,inf,1);
    }
    insert(1,n,inf,1),insert(n,1,inf,1);
//  for (int i=2;i<=te;i+=2)
//  cout<<e[i].u<<' '<<e[i].v<<' '<<e[i].cap<<' '<<e[i].cost<<endl;
    int cost;
    mcmf(cost);
    cout<<cost;
    return 0;
}