蓝桥杯 算法训练 Remember the A La Mode

费用流裸题

要注意的是浮点数判断

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=100005;
int cur[N],head[N],vis[N];
double dis[N];
const double inf=0x7fffffff;
const double eps=1e-6;
struct ss
{
    int u,v;
    int w;
    double val;
}e[N];
int n,m,s,t,cnt=1;
int aa[555];
int bb[555];
double cc[55][55];
double ret=0;
inline void add(int u,int v,int w,double val)
{
    cnt++;
    e[cnt].v=v;
    e[cnt].w=w;
    e[cnt].val=val;
    e[cnt].u=head[u];
    head[u]=cnt;
}
inline void addedge(int u,int v,int w,double val)
{
    add(u,v,w,val);
    add(v,u,0,-val);
}
inline int spfa()
{
    for(int i=s;i<=t;++i)dis[i]=inf;
    vis[s]=1;
    dis[s]=0;
    queue<int>q;
    while(!q.empty())q.pop();
    q.push(s);
    while(q.size())
    {
        int u=q.front();
        q.pop();
        vis[u]=0;
        for(int i=head[u];i;i=e[i].u)
        {
            int v=e[i].v;
            int w=e[i].w;
            //if(w&&dis[v]>dis[u]+e[i].val)
            if(w&&((dis[v]-(dis[u]+e[i].val))>eps))
            {
                dis[v]=dis[u]+e[i].val;
                if(!vis[v])
                {
                    vis[v]=1;
                    q.push(v);
                }
            }
        }
    }
    return fabs(inf-dis[t])<eps?0:1;//dis[t]!=inf;
}
inline int dfs(int u,int flow)
{
    if(u==t)return flow;
    int rest=flow;
    vis[u]=1;
    for(int i=cur[u];i&&rest;i=e[i].u)
    {
        cur[u]=i;
        int v=e[i].v;
        int w=e[i].w;
        if(w&&!vis[v]&&(fabs(dis[v]-(dis[u]+e[i].val))<eps))
        {
            int k=dfs(v,min(w,rest));
            if(k)
            {
                ret+=k*e[i].val;
                e[i].w-=k;
                e[i^1].w+=k;
                rest-=k;
            }
        }
    }
    vis[u]=0;
    return flow-rest;
}
int main()
{
    scanf("%d%d",&n,&m);
    s=0;t=n+m+1;
    for(int i=1;i<=n;++i)
    {
        scanf("%d",&aa[i]);
        addedge(s,i,aa[i],0);
    }
    for(int i=1;i<=m;++i)
    {
        scanf("%d",&bb[i]);
        addedge(i+n,t,bb[i],0);
    }
    for(int i=1;i<=n;++i)
    {
        for(int j=1;j<=m;++j)
        {
            scanf("%lf",&cc[i][j]);
            if(fabs(cc[i][j]+1)<eps)continue;
            addedge(i,j+n,aa[i],cc[i][j]);
        }
    }
    while(spfa())
    {
        for(int i=s;i<=t;++i)cur[i]=head[i];
        dfs(s,inf);
    }
    printf("%.2f to ",ret);
    cnt=1;
    ret=0;
    for(int i=s;i<=t;++i)head[i]=0;
    for(int i=1;i<=n;++i)addedge(s,i,aa[i],0);
    for(int i=1;i<=m;++i)addedge(i+n,t,bb[i],0);
    for(int i=1;i<=n;++i)
    {
        for(int j=1;j<=m;++j)
        {
            if(fabs(cc[i][j]+1)<eps)continue;
            addedge(i,j+n,aa[i],-cc[i][j]);
        }
    }
    while(spfa())
    {
        for(int i=s;i<=t;++i)cur[i]=head[i];
        dfs(s,inf);
    }
    printf("%.2f\n",-ret);
    return 0;
}