bzoj2055

题解：

似乎是放在费用流里的

然而是有上下界的网络流QAQ

代码：

#include<bits/stdc++.h>
using namespace std;
const int N=40005;
int n,m,x,mincost,s,t,S,ss,tt,tot,fi[N],ne[N],zz[N],sl[N],c[N];
int dis[N],last[N],d[N],vis[N];
queue <int> q;
void jb(int x,int y,int cap,int z)
{
    ne[++tot]=fi[x];
    fi[x]=tot;
    zz[tot]=y;
    sl[tot]=cap;
    c[tot]=z;
    ne[++tot]=fi[y];
    fi[y]=tot;
    zz[tot]=x;
    sl[tot]=0;
    c[tot]=-z;
}
int addflow(int s,int t)
{
    int now=t,ans=1e9;
    while (now!=s)
     {
        ans=min(ans,sl[last[now]]);
        now=zz[last[now]^1];
     }
    now=t;
    while (now!=s)
     {
        sl[last[now]]-=ans;
        sl[last[now]^1]+=ans;
        now=zz[last[now]^1];
     }
    return ans;
}
int spfa(int s,int t)
{
    memset(dis,127,sizeof(dis));
    dis[s]=0;
    memset(vis,0,sizeof(vis));
    vis[s]=1;
    while (!q.empty())q.pop();
    q.push(s);
    while (!q.empty())
     {
        int now=q.front();q.pop();
        vis[now]=0;
        for (int i=fi[now];i!=-1;i=ne[i])
         if (dis[zz[i]]>dis[now]+c[i]&&sl[i])
          {
            dis[zz[i]]=dis[now]+c[i];
            last[zz[i]]=i;
            if (!vis[zz[i]])
             {
                vis[zz[i]]=1;
                q.push(zz[i]);
             }
          }
     }
    if (dis[t]>1e9) return 0;
    int flow=addflow(s,t);
    mincost+=flow*dis[t];
    return 1;
}
int main()
{
    tot=-1;
    memset(fi,-1,sizeof(fi));
    scanf("%d%d",&n,&m);
    S=n+n+1,s=S+1,t=s+1;ss=t+1,tt=ss+1;
    d[s]-=m,d[S]+=m;
    for (int i=1;i<=n;i++)
     {
        scanf("%d",&x);
        jb(S,i,1e9,0);
        jb(n+i,t,1e9,0);
        d[i]-=x,d[n+i]+=x;
     }
    for (int i=1;i<n;i++)
     for (int j=i+1;j<=n;j++)
      {
        scanf("%d",&x);
        if (x==-1) continue;
        jb(n+i,j,1e9,x);
      }
    for (int i=1;i<=t;i++)
     {
        if (d[i]>0)jb(ss,i,d[i],0);
        if (d[i]<0)jb(i,tt,-d[i],0);
     }
    jb(t,s,1e9,0);
    while (spfa(ss,tt));
    printf("%d
",mincost);
}