网络流初步——增广路算法（EK）模板

Posted 2020-07-26 wls001

 1 #include <iostream>
 2 #include <queue>
 3 #include<string.h>
 4 using namespace std;
 5 #define arraysize 201
 6 int maxData = 0x7fffffff;
 7 int a[222][222];
 8 int flow[222];
 9 int pre[222];
10 int n,m;
11 queue<int> q;
12 int BFS(int s,int t)
13 {
14     int i,j;
15     while(!q.empty())
16         q.pop();
17     for(i=1;i<m+1;i++)
18     {
19         pre[i]=-1;
20     }
21     pre[s]=0;
22     flow[s]= maxData;
23     q.push(s);
24     while(!q.empty())
25     {
26         int index=q.front();
27         q.pop();
28         if(index==t)
29             break;
30         for(i=1;i<m+1;++i)
31         {
32             if(i!=s && a[index][i]>0 && pre[i]==-1)
33             {
34                  pre[i]=index;
35                  flow[i]=min(a[index][i],flow[index]);
36                  q.push(i);
37             }
38         }
39     }
40     if(pre[t]==-1)
41         return -1;
42     else
43         return flow[t];
44 }
45 int ek(int s,int t)
46 {
47     int increasement=0;
48     int sumflow=0;
49     while((increasement=BFS(s,t))!=-1)
50     {
51          int k=t;
52          while(k!=s)
53          {
54               int last=pre[k];
55               a[last][k]-=increasement;
56               a[k][last]+=increasement;
57               k = last;
58          }
59          sumflow+=increasement;
60     }
61     return sumflow;
62 }
63 int main()
64 {
65     int i,j;
66     int start,end,ci;
67     cin>>n>>m;
68     memset(a,0,sizeof(a));
69     memset(flow,0,sizeof(flow));
70     for(i=0;i<n;i++)
71     {
72         cin>>start>>end>>ci;
73         a[start][end]+=ci;
74     }
75     cout<<ek(1,m)<<endl;
76     return 0;
77 }

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