HDU 5988最小网络流（浮点数）

题目链接：http://acm.split.hdu.edu.cn/showproblem.php?pid=5988

哇，以前的模版一直T，加了优先队列优化才擦边过。

建图很好建，概率乘法化成概率加法不会化。

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <vector>
 #include <queue>
 #include <algorithm>
 #include <cmath>
 using namespace std;
 const int maxn = ;
 const int INF = 1e9;
 double dist[maxn];
 int tot,head[maxn];
 int pv[maxn],pe[maxn];
 typedef pair<double,int> P;
 double eps = 1e-;
 struct edge
 {
     int to,pre,cap;
     double cost;
 }e[];
 void init()
 {
     tot = ;
     memset(head,-,sizeof(head));
 }
 void add(int from,int to,int cap,double cost)
 {
     e[tot].pre = head[from];
     e[tot].to = to;
     e[tot].cap = cap;
     e[tot].cost = cost;
     head[from] = tot++;
 }
 void addedge(int from,int to,int cap,double cost)
 {
     add(from,to,cap,cost);
     add(to,from,,-cost);
 }
 int n;
 double min_cost_flow(int s,int t,int f,int& max_flow)
 {
     double ret = 0.0;
     while(f>)
     {
         priority_queue<P,vector<P>,greater<P> >q;
         for(int i=;i<maxn;i++) dist[i] = INF;
         dist[s] = 0.0;
         q.push(P(,s));
         while(!q.empty())
         {
             P cur = q.top(); q.pop();
             int v = cur.second;
             if(dist[v]<cur.first) continue;
             for(int i=head[v];i>=;i=e[i].pre)
             {
                 int to = e[i].to,cap = e[i].cap;
                 double cost = e[i].cost;
                 if(cap>&&(dist[to]-(dist[v]+cost))>=eps)
                 {
                     pv[to] = v,pe[to] = i;
                     dist[to] = dist[v] + cost;
                     q.push(P(dist[to],to));
                 }
             }
         }
         if(fabs(dist[t]-INF)<=eps) return ret;///同一目的地，每次增广路都是最小费用
         ///当所有边的流量都流净后，即没有残余网络，返回。
         int d = f;
         for(int v=t;v!=s;v=pv[v])
         {
             d = min(d,e[pe[v]].cap);
         }
         f -= d;
         max_flow += d;
         ret += (double)d*dist[t]; ///走一单位就消耗dist[t]
         for(int v=t;v!=s;v=pv[v])
         {
             e[pe[v]].cap -= d;
             e[pe[v]^].cap += d;
         }
     }
     return ret;
 }
 int main()
 {
     int T;scanf("%d",&T);
     while(T--)
     {
         int m;
         init();
         scanf("%d %d",&n,&m);
         int s = n+;
         int t = n+;
         for(int i=;i<=n;i++)
         {
             int si,bi;
             scanf("%d %d",&si,&bi);
             int x = si-bi;
             if(x>) addedge(s,i,x,);
             else if(x<) addedge(i,t,-x,);
         }
         int u,v,c;
         double p;
         for(int i=;i<=m;i++)
         {
             scanf("%d %d %d %lf",&u,&v,&c,&p);
             p = -1.0*log2(1.0-p);
             if(c>)
             {
                 addedge(u,v,,);///第一个人不用费用
             }
             if(c->)
             {
                 addedge(u,v,c-,p);
             }
         }
         int max_flow = ;
         double cost =  min_cost_flow(s,t,INF,max_flow);
         double di = 2.0;
         printf("%.2f\n",(1.0-pow(di,-cost)));
     }
     return ;
 }