poj 1273 最大流入门

明天再拍一遍

 1 #include <iostream>

 2 #include <queue>

 3 using namespace std;

 4 const int N = 210;

 5 const int INF = 0x7FFFFFFF;

 6 int n,m,map[N][N],path[N],flow[N],start,end;

 7 queue<int> q;

 8 int bfs()

 9 {

10     int i,t;

11     while(!q.empty()) q.pop();

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

13     path[start]=0,flow[start]=INF;

14     q.push(start);

15     while(!q.empty())

16     {

17         t=q.front();

18         q.pop();

19         if(t==end) break;

20         for(i=1;i<=m;i++)

21         {

22             if(i!=start && path[i]==-1 && map[t][i])

23             {

24                 flow[i]=flow[t]<map[t][i]?flow[t]:map[t][i];

25                 q.push(i);

26                 path[i]=t;

27             }

28         }

29     }

30     if(path[end]==-1) return -1;

31     return flow[m];                   //一次遍历之后的流量增量

32 }

33 int Edmonds_Karp()

34 {

35     int max_flow=0,step,now,pre;

36     while((step=bfs())!=-1)

37     {          //找不到增路径时退出

38         max_flow+=step;

39         now=end;

40         while(now!=start)

41         {

42             pre=path[now];

43             map[pre][now]-=step;      //更新正向边的实际容量

44             map[now][pre]+=step;      //添加反向边

45             now=pre;

46         }

47     }

48     return max_flow;

49 }

50  int main()

51  {

52     int i,u,v,cost;

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

54     {

55         memset(map,0,sizeof(map));

56         for(i=0;i<n;i++)

57         {

58             scanf("%d %d %d",&u,&v,&cost);

59             map[u][v]+=cost;           //not just only one input

60         }

61         start=1,end=m;

62         printf("%d\n",Edmonds_Karp());

63     }

64     return 0;

65 }