UVa820 Internet Bandwidth
最大流模板。
1 #include <cstdio>
2 #include <cstring>
3 #include <algorithm>
4 #include <vector>
5 #include <queue>
6 #include <iostream>
7 using namespace std;
8 const int MAXN = 100 + 20;
9 const int INF = 0x3f3f3f3f;
10
11 int N, S, T, C;
12
13 namespace dinic
14 {
15 struct edge
16 {
17 int to, cap, rev;
18 edge(int v = 0, int c = 0, int r = 0) :
19 to(v), cap(c), rev(r) {}
20 };
21 vector<edge> g[MAXN];
22 int level[MAXN], iter[MAXN];
23
24 inline void init()
25 {
26 for(int i = 0; i <= N; i++)
27 g[i].clear();
28 memset(level, 0, sizeof(level));
29 memset(iter, 0, sizeof(iter));
30 }
31
32 inline void addedge(int u, int v, int c)
33 {
34 g[u].push_back(edge(v, c, g[v].size()));
35 g[v].push_back(edge(u, c, g[u].size() - 1));
36 }
37
38 inline bool bfs()
39 {
40 queue<int> q;
41 memset(level, -1, sizeof(level));
42 q.push(S);
43 level[S] = 0;
44
45 while(!q.empty())
46 {
47 int u = q.front(); q.pop();
48 for(int i = 0; i < (int) g[u].size(); i++)
49 {
50 edge e = g[u][i];
51 if(e.cap && level[e.to] == -1)
52 {
53 level[e.to] = level[u] + 1;
54 q.push(e.to);
55 }
56 }
57 }
58 return ~level[T];
59 }
60
61 int dfs(int u, int flow)
62 {
63 if(u == T) return flow;
64
65 for(int &i = iter[u]; i < (int) g[u].size(); i++)
66 {
67 edge &e = g[u][i];
68 if(e.cap && level[e.to] == level[u] + 1)
69 {
70 int d = dfs(e.to, min(flow, e.cap));
71 if(d)
72 {
73 e.cap -= d;
74 g[e.to][e.rev].cap += d;
75 return d;
76 }
77 }
78 }
79 return 0;
80 }
81
82 int maxflow()
83 {
84 int d = 0, flow = 0;
85 while(bfs())
86 {
87 memset(iter, 0, sizeof(iter));
88 while(d = dfs(S, INF), d) flow += d;
89 }
90 return flow;
91 }
92 }
93
94 int main()
95 {
96 //freopen("820.in", "r", stdin);
97 //freopen("820.out", "w", stdout);
98 int cnt = 0;
99 while(cin>>N, N)
100 {
101 cnt++;
102
103 dinic::init();
104 cin>>S>>T>>C;
105 int u, v, c;
106 for(int i = 1; i <= C; i++)
107 {
108 scanf(" %d %d %d", &u, &v, &c);
109 dinic::addedge(u, v, c);
110 }
111
112 printf("Network %d\n", cnt);
113 printf("The bandwidth is %d.\n", dinic::maxflow());
114 puts("");
115 }
116 return 0;
117 }
