poj2455Secret Milking Machine(二分+最大流）

链接

二分距离，小于当前距离的边容量+1，使最后流>=t

注意 会有重边

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 205
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 int path[N],flow[N],gh[N][N],st,en;
 int w[N][N];
 struct node
 {
     int u,v,c;
 }q[N*N];
 int bfs()
 {
     int i;
     memset(path,-,sizeof(path));
     for(i =  ; i <= en ; i++)
     flow[i] = INF;
     queue<int>q;
     q.push();
     while(!q.empty())
     {
         int tk = q.front();
         q.pop();
         if(tk==en)
         break;
         for(i =  ; i <= en ; i++)
         {
             if(path[i]==-&&gh[tk][i])
             {
                 path[i] = tk;
                 flow[i] = min(flow[tk],gh[tk][i]);
                 q.push(i);
             }
         }
     }
     if(path[en]==-)
     return -;
     return flow[en];
 }
 int EK()
 {
     int now,pre,sum=,k;
     while((k=bfs())!=-)
     {
         sum+=k;
         now = en;
         while(now!=st)
         {
             pre = path[now];
             gh[pre][now]-=k;
             gh[now][pre]+=k;
             now = pre;
         }
     }
     return sum;
 }
 int main()
 {
     int n,p,i,m;
     while(scanf("%d%d%d",&n,&p,&m)!=EOF)
     {
         for(i = ; i <= p ;i++)
         {
             scanf("%d%d%d",&q[i].u,&q[i].v,&q[i].c);
             q[i].u++,q[i].v++;
         }
         st = ;
         en = n+;
         int low = ,high = ,mid;
         while(low<=high)
         {
             mid = (low+high)>>;
             memset(gh,,sizeof(gh));
             gh[st][] = m;
             gh[n+][en] = m;
             for(i = ;i <= p ; i++)
             if(q[i].c<=mid)
             {
                 gh[q[i].u][q[i].v]+=;
                 gh[q[i].v][q[i].u]+=;
             }
             if(EK()==m)
             high = mid-;
             else
             low =mid+;
         }
         cout<<low<<endl;
     }
     return ;
 }