BZOJ 3993 星际战争

二分+最大流 。

eps要设1e-7。。。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#define maxv 205
#define maxe 1000050
#define inf 1000000007
#define eps 1e-7
using namespace std;
int n,m,a[maxv],b[maxv],g[maxv],nume=1,dis[maxv],map[maxv][maxv],s,t;
struct edge
{
    int v,nxt;
    double f;
}e[maxe];
double sum=0,max_flow;
queue <int> q;
void addedge(int u,int v,double f)
{
    e[++nume].v=v;e[nume].f=f;e[nume].nxt=g[u];g[u]=nume;
    e[++nume].v=u;e[nume].f=0;e[nume].nxt=g[v];g[v]=nume;
}
void build(double x)
{
    s=0;t=n+m+1;memset(g,0,sizeof(g));nume=1;
    for (int i=1;i<=m;i++) addedge(s,i,(double)b[i]*x);
    for (int i=1;i<=n;i++) addedge(i+m,t,a[i]);
    for (int i=1;i<=m;i++)
        for (int j=1;j<=n;j++)    
            if (map[i][j]) addedge(i,j+m,inf);
}
bool bfs()
{
    for (int i=s;i<=t;i++) dis[i]=inf;dis[s]=0;q.push(s);
    while (!q.empty())
    {
        int head=q.front();q.pop();
        for (int i=g[head];i;i=e[i].nxt)
        {
            int v=e[i].v;
            if (fabs(e[i].f)>eps && dis[v]>dis[head]+1)
            {
                dis[v]=dis[head]+1;
                q.push(v);
            }
        }
    }
    return dis[t]!=inf;
}
double dinic(int x,double low)
{
    if (x==t) return low;
    double ret=0.0;
    for (int i=g[x];i && (low>0.0);i=e[i].nxt)
    {
        int v=e[i].v;
        if (fabs(e[i].f)>eps && dis[v]==dis[x]+1)
        {
            double dd=dinic(v,min(low,e[i].f));
            ret+=dd;low-=dd;e[i].f-=dd;e[i^1].f+=dd;
        }
    }
    if (fabs(ret)<eps) dis[x]=inf;
    return ret;
}
bool check(double t)
{
    max_flow=0.0;build(t);
    while (bfs()) max_flow+=dinic(s,inf);
    return fabs(max_flow-sum)<eps;
}
double DC()
{
    double l=0,r=inf,mid,ans;
    while (r-l>eps)
    {
        mid=(l+r)/2;
        if (check(mid)) ans=r=mid;
        else l=mid;
    }
    return ans;
}
int main()
{
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n;i++) {scanf("%d",&a[i]);sum+=(double)a[i];}
    for (int i=1;i<=m;i++) scanf("%d",&b[i]);
    for (int i=1;i<=m;i++)
        for (int j=1;j<=n;j++)
            scanf("%d",&map[i][j]);
    printf("%.6lf
",DC());
    return 0;
}