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

  1 #include <iostream>

  2 #include<cstdio>

  3 #include<cstring>

  4 #include<algorithm>

  5 #include<stdlib.h>

  6 #include<vector>

  7 #include<cmath>

  8 #include<queue>

  9 #include<set>

 10 using namespace std;

 11 #define N 205

 12 #define LL long long

 13 #define INF 0xfffffff

 14 const double eps = 1e-8;

 15 const double pi = acos(-1.0);

 16 const double inf = ~0u>>2;

 17 int path[N],flow[N],gh[N][N],st,en;

 18 int w[N][N];

 19 struct node

 20 {

 21     int u,v,c;

 22 }q[N*N];

 23 int bfs()

 24 {

 25     int i;

 26     memset(path,-1,sizeof(path));

 27     for(i = 1 ; i <= en ; i++)

 28     flow[i] = INF;

 29     queue<int>q;

 30     q.push(1);

 31     while(!q.empty())

 32     {

 33         int tk = q.front();

 34         q.pop();

 35         if(tk==en)

 36         break;

 37         for(i = 1 ; i <= en ; i++)

 38         {

 39             if(path[i]==-1&&gh[tk][i])

 40             {

 41                 path[i] = tk;

 42                 flow[i] = min(flow[tk],gh[tk][i]);

 43                 q.push(i);

 44             }

 45         }

 46     }

 47     if(path[en]==-1)

 48     return -1;

 49     return flow[en];

 50 }

 51 int EK()

 52 {

 53     int now,pre,sum=0,k;

 54     while((k=bfs())!=-1)

 55     {

 56         sum+=k;

 57         now = en;

 58         while(now!=st)

 59         {

 60             pre = path[now];

 61             gh[pre][now]-=k;

 62             gh[now][pre]+=k;

 63             now = pre;

 64         }

 65     }

 66     return sum;

 67 }

 68 int main()

 69 {

 70     int n,p,i,m;

 71     while(scanf("%d%d%d",&n,&p,&m)!=EOF)

 72     {

 73         for(i = 1; i <= p ;i++)

 74         {

 75             scanf("%d%d%d",&q[i].u,&q[i].v,&q[i].c);

 76             q[i].u++,q[i].v++;

 77         }

 78         st = 1;

 79         en = n+2;

 80         int low = 0,high = 1000000,mid;

 81         while(low<=high)

 82         {

 83             mid = (low+high)>>1;

 84             memset(gh,0,sizeof(gh));

 85             gh[st][2] = m;

 86             gh[n+1][en] = m;

 87             for(i = 1;i <= p ; i++)

 88             if(q[i].c<=mid)

 89             {

 90                 gh[q[i].u][q[i].v]+=1;

 91                 gh[q[i].v][q[i].u]+=1;

 92             }

 93             if(EK()==m)

 94             high = mid-1;

 95             else

 96             low =mid+1;

 97         }

 98         cout<<low<<endl;

 99     }

100     return 0;

101 }

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