POJ 1273 (基础最大流) Drainage Ditches

虽然算法还没有理解透，但以及迫不及待地想要A道题了。

非常裸的最大流，试试lrj的模板练练手。

 1 #include <cstdio>

 2 #include <cstring>

 3 #include <algorithm>

 4 #include <vector>

 5 #include <queue>

 6 using namespace std;

 7 

 8 const int maxn = 200 + 10;

 9 const int INF = 1000000000;

10 

11 struct Edge

12 {

13     int from, to, cap, flow;

14     Edge(int u, int v, int c, int f):from(u), to(v), cap(c), flow(f) {}

15 };

16 

17 int n, m, M;

18 vector<Edge> edges;

19 vector<int> G[maxn];

20 int a[maxn];    //到起点i的可改进量

21 int p[maxn];    //最短路数上p的入弧编号

22 

23 void Init(int n)

24 {

25     for(int i = 0; i < n; ++i) G[i].clear();

26     edges.clear();

27 }

28 

29 void AddEdge(int from, int to, int cap)

30 {

31     edges.push_back(Edge(from, to, cap, 0));

32     edges.push_back(Edge(to, from, 0, 0));    //反向弧

33     m = edges.size();

34     G[from].push_back(m-2);

35     G[to].push_back(m-1);

36 }

37 

38 int MaxFlow(int s, int t)

39 {

40     int flow = 0;

41     for(;;)

42     {

43         memset(a, 0, sizeof(a));

44         queue<int> Q;

45         Q.push(s);

46         a[s] = INF;

47         while(!Q.empty())

48         {

49             int x = Q.front(); Q.pop();

50             for(int i = 0; i < G[x].size(); ++i)

51             {

52                 Edge& e = edges[G[x][i]];

53                 if(!a[e.to] && e.cap > e.flow)

54                 {

55                     p[e.to] = G[x][i];

56                     a[e.to] = min(a[x], e.cap-e.flow);

57                     Q.push(e.to);

58                 }

59             }

60             if(a[t]) break;

61         }

62         if(!a[t]) break;

63         for(int u = t; u != s; u = edges[p[u]].from)

64         {

65             edges[p[u]].flow += a[t];

66             edges[p[u]^1].flow -= a[t];

67         }

68         flow += a[t];

69     }

70     return flow;

71 }

72 

73 int main()

74 {

75     freopen("in.txt", "r", stdin);

76 

77     while(scanf("%d%d", &M, &n) == 2)

78     {

79         Init(n);

80         int u, v, c;

81         for(int i = 0; i < M; ++i)

82         {

83             scanf("%d%d%d", &u, &v, &c);

84             AddEdge(u-1, v-1, c);

85         }

86         printf("%d\n", MaxFlow(0, n-1));

87     }

88 

89     return 0;

90 }

代码君