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=;

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]=;

    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]^];

     }

    now=t;

    while (now!=s)

     {

        sl[last[now]]-=ans;

        sl[last[now]^]+=ans;

        now=zz[last[now]^];

     }

    return ans;

}

int spfa(int s,int t)

{

    memset(dis,,sizeof(dis));

    dis[s]=;

    memset(vis,,sizeof(vis));

    vis[s]=;

    while (!q.empty())q.pop();

    q.push(s);

    while (!q.empty())

     {

        int now=q.front();q.pop();

        vis[now]=;

        for (int i=fi[now];i!=-;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]]=;

                q.push(zz[i]);

             }

          }

     }

    if (dis[t]>1e9) return ;

    int flow=addflow(s,t);

    mincost+=flow*dis[t];

    return ;

}

int main()

{

    tot=-;

    memset(fi,-,sizeof(fi));

    scanf("%d%d",&n,&m);

    S=n+n+,s=S+,t=s+;ss=t+,tt=ss+;

    d[s]-=m,d[S]+=m;

    for (int i=;i<=n;i++)

     {

        scanf("%d",&x);

        jb(S,i,1e9,);

        jb(n+i,t,1e9,);

        d[i]-=x,d[n+i]+=x;

     }

    for (int i=;i<n;i++)

     for (int j=i+;j<=n;j++)

      {

        scanf("%d",&x);

        if (x==-) continue;

        jb(n+i,j,1e9,x);

      }

    for (int i=;i<=t;i++)

     {

        if (d[i]>)jb(ss,i,d[i],);

        if (d[i]<)jb(i,tt,-d[i],);

     }

    jb(t,s,1e9,);

    while (spfa(ss,tt));

    printf("%d\n",mincost);

}