BZOJ3993: [SDOI2015]星际战争

题目：http://www.lydsy.com/JudgeOnline/problem.php?id=3993

二分最大流就可以了。

#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<set>
#include<cmath>
#define rep(i,l,r) for (int i=l;i<=r;i++)
#define down(i,l,r) for (int i=l;i>=r;i--)
#define clr(x,y) memset(x,y,sizeof(x))
#define maxn 3005
#define inf 1e9
#define mm 1000000007
#define eps 1e-7
typedef long long ll;
using namespace std;
struct data{int obj,pre;double c;
}e[maxn*2];
int tot,n,m,t,head[maxn],uu[maxn],cur[maxn],mp[60][60];
double sum,a[maxn],b[maxn];
int read(){
    int x=0,f=1; char ch=getchar();
    while (!isdigit(ch)){if (ch=='-') f=-1; ch=getchar();}
    while (isdigit(ch)){x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}   
void insert(int x,int y,double z){
    e[++tot].obj=y; e[tot].pre=head[x]; e[tot].c=z; head[x]=tot; 
    e[++tot].obj=x; e[tot].pre=head[y]; e[tot].c=0; head[y]=tot;
}
bool bfs(){
    clr(uu,-1); uu[0]=0;
    queue<int> q; q.push(0);
    while (!q.empty()){
        int u=q.front(); q.pop();
        for (int j=head[u];j;j=e[j].pre){
            int v=e[j].obj;
            if (e[j].c>eps&&uu[v]==-1) uu[v]=uu[u]+1,q.push(v);
        }
    }
    return uu[t]!=-1;
}
double dfs(int x,double mx){
    double used=0;
    if (x==t) return mx;
    for (int j=head[x];j;j=e[j].pre){
        int v=e[j].obj;
        if (uu[v]==uu[x]+1&&fabs(e[j].c)>eps){
            double w=dfs(v,min(e[j].c,mx-used));
            used+=w; e[j].c-=w; e[j^1].c+=w;
            if (fabs(e[j].c)>eps) cur[x]=j;
            if (fabs(mx-used)<=eps) return used;
        }
    }
    if (used<=eps) uu[x]=-1;
    return used;
}
double dinic(){
    double ans=0;
    while (bfs()){
        rep(i,0,t) cur[i]=head[i];
        ans+=dfs(0,inf);
        //printf("%.3lf
",ans);
    }
    return ans;
}
bool jud(double mid){
    clr(head,0); tot=1;
    rep(i,1,m) insert(0,i,b[i]*mid);
    rep(i,1,n) insert(i+m,t,a[i]);
    rep(i,1,m) rep(j,1,n) if (mp[i][j]) insert(i,j+m,inf);
    if (dinic()>=(sum-eps)) return 1;
    return 0;
}
int main(){
//  freopen("in.txt","r",stdin);
    n=read(); m=read();
    rep(i,1,n) scanf("%lf",&a[i]),sum+=a[i];
    rep(i,1,m) scanf("%lf",&b[i]);
    rep(i,1,m) rep(j,1,n) mp[i][j]=read();
    t=n+m+1;
    double l=0,r=inf;
    while (fabs(r-l)>eps){
        double mid=(l+r)/2;
        if (jud(mid)) r=mid;
        else l=mid;
    }
    printf("%.6lf
",l);
    return 0;
}