HDU3549+Ford-Fulkerson

Ford-Fulkerson算法

基本没什么技巧

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 1 #include<cstdio>

 2 #include<cstring>

 3 #include<cstdlib>

 4 #include<queue>

 5 using namespace std;

 6 #define N 1005

 7 #define inf 9999999

 8 int map[N][N],pre[N],vis[N];

 9 int start,eend,ans;

10 

11 void max_flow(int n)

12 {

13     int i,j,k;

14     while(1)

15     {

16         queue<int>q;

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

18 

19         memset(vis,0,sizeof(vis));

20         //memset(pre,-1,sizeof(pre));

21 

22         q.push(start);

23         vis[start]=1;

24         while(!q.empty())

25         {

26             k=q.front();

27             q.pop();

28             if(k==eend) break;//找到了增广路

29             for(i=1;i<=n;i++)

30             {

31                 if(vis[i]==1||map[k][i]==0)continue;

32                 q.push(i);

33                 vis[i]=1;

34                 pre[i]=k;

35             }

36         }

37 

38         if(vis[eend]==0)break;//无法找到增广路

39 

40         int min=inf;

41         for(i=eend;i!=start;i=pre[i])

42         {

43             if(map[pre[i]][i]<min)

44             {

45                 min=map[pre[i]][i];

46             }

47         }

48 

49         for(i=eend;i!=start;i=pre[i])

50         {

51             map[pre[i]][i]-=min;

52             map[i][pre[i]]+=min;

53         }

54         ans+=min;

55     }

56     return ;

57 }

58 

59 int main()

60 {

61     int i,j,k,tcase,t;

62     int m,n,a,b,c;

63     scanf("%d",&tcase);

64     for(t=1;t<=tcase;t++)

65     {

66         scanf("%d%d",&n,&m);

67         start=1;

68         eend=n;

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

70         while(m--)

71         {

72             scanf("%d%d%d",&a,&b,&c);

73             map[a][b]+=c;

74         }

75         ans=0;

76         max_flow(n);

77         printf("Case %d: %d\n",t,ans);

78     }

79     return 0;

80 }