最大流基础

QC的博客搬来http://www.cnblogs.com/pony1993/archive/2012/07/28/2612883.html

模板题poj1273http://www.cnblogs.com/pony1993/archive/2012/07/28/2612883.html

代码

View Code

 1 #include <iostream>

 2 #include<cstdio>

 3 #include<cstring>

 4 #include<algorithm>

 5 #include<queue>

 6 #define INF 0x3f3f3f

 7 using namespace std;

 8 int n,m,path[210],map[210][210],flow[210],st,en;

 9 int bfs()

10 {

11     int i,j,k;

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

13     path[st] = 0;

14     flow[st]= INF;

15     queue<int>q;

16     q.push(st);

17     while(!q.empty())

18     {

19         int mt = q.front();

20         q.pop();

21         if(mt==en)

22         break;

23         for(i = 1; i <= m ; i++)//找到新节点

24         {

25             if(i!=st&&path[i]==-1&&map[mt][i])

26             {

27                 flow[i] = min(flow[mt],map[mt][i]);//路径上的最小残量

28                 q.push(i);

29                 path[i] = mt;

30             }

31         }

32     }

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

34     return -1;

35     return flow[en];

36 }

37 int karp()

38 {

39     int i,j,k,ml = 0,now,pre;

40     while((k=bfs())!=-1)//bfs找增广路径

41     {

42         ml+=k;

43         now = en;

44         while(now!=st)

45         {

46             pre = path[now];//path保留节点的前驱  更新正向边的实际容量

47             map[pre][now]-=k;

48             map[now][pre]+=k;//增加逆向边的容量

49             now = pre;

50         }

51     }

52     return ml;

53 }

54 int main()

55 {

56     int i,j,k,g,a,b,c;

57     while(cin>>n>>m)

58     {

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

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

61         {

62             cin>>a>>b>>c;

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

64         }

65         st = 1,en = m;

66         cout<<karp()<<endl;

67     }

68     return 0;

69 }

 多源点最大流

pojhttp://poj.org/problem?id=1459

增加一个源点与核电站相连 一个终点与c相连 d看做平常的节点

View Code

 1 #include <iostream>

 2 #include<cstdio>

 3 #include<cstring>

 4 #include<algorithm>

 5 #include<queue>

 6 #define INF 0x3f3f3f

 7 using namespace std;

 8 int path[110],map[110][110],flow[110],en,st,m;

 9 int bfs()

10 {

11     int i,j,k;

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

13     path[st] = 0;

14     flow[st] = INF;

15     queue<int>q;

16     q.push(st);

17     while(!q.empty())

18     {

19         int mt = q.front();

20         q.pop();

21         if(mt==en)

22         break;

23         for(i = 0; i <= en ; i++)

24         {

25             if(i!=st&&path[i]==-1&&map[mt][i])

26             {

27                 path[i] = mt;

28                 flow[i] = min(flow[mt],map[mt][i]);

29                 q.push(i);

30 

31             }

32         }

33     }

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

35     return -1;

36     return flow[en];

37 }

38 int karp()

39 {

40     int i,j,k,now,ml=0,pre;

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

42     {

43         ml+=k;

44         now = en;

45         while(now!=st)

46         {

47             pre = path[now];

48             map[pre][now]-=k;

49             map[now][pre]+=k;

50             now = pre;

51         }

52     }

53     return ml;

54 }

55 int main()

56 {

57     int i,j,k,g,n,nc,np,u,v,w;

58     char str[20],c1,c2,c3;

59     while(cin>>n>>np>>nc>>m)

60     {

61         getchar();

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

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

64         {

65             cin>>c1>>u>>c2>>v>>c3>>w;

66             map[u][v] += w;

67         }

68         for(i = 1; i <= np ; i++)

69         {

70             cin>>c1>>u>>c2>>w;

71             map[n][u] += w;

72         }

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

74         {

75             cin>>c1>>u>>c2>>w;

76             map[u][n+1] += w;

77         }

78         st = n;

79         en = n+1;

80         cout<<karp()<<endl;

81     }

82     return 0;

83 }