UVa1660 Cable TV Network (无向图,点连通度,最大流)

 1 #include <cstdio>
 2 #include <queue>
 3 #include <cstring>
 4 #include <vector>
 5 using namespace std;
 6 
 7 const int maxn = 100 + 5;
 8 const int INF = 0x3f3f3f3f;
 9 
10 struct Edge {
11     int from, to, cap, flow;
12     Edge(int u, int v, int c, int f):from(u), to(v), cap(c), flow(f) {}
13 };
14 
15 struct EdmondsKarp {
16     int n, m;
17     vector<Edge> edges;
18     vector<int> G[maxn];
19     int a[maxn];
20     int p[maxn];
21 
22     void init(int n) {
23         for (int i = 0; i < n; i++) G[i].clear();
24         edges.clear();
25     }
26 
27     void AddEdge(int from, int to, int cap) {
28         edges.push_back(Edge(from, to, cap, 0));
29         edges.push_back(Edge(to, from, 0, 0));
30         m = edges.size();
31         G[from].push_back(m - 2);
32         G[to].push_back(m - 1);
33     }
34 
35     int Maxflow(int s, int t) {
36         int flow = 0;
37         for (;;) {
38             memset(a, 0, sizeof(a));
39             queue<int> Q;
40             Q.push(s);
41             a[s] = INF;
42             while (!Q.empty()) {
43                 int x = Q.front(); Q.pop();
44                 for (int i = 0; i < G[x].size(); i++) {
45                     Edge& e = edges[G[x][i]];
46                     if (!a[e.to] && e.cap > e.flow) {
47                         p[e.to] = G[x][i];
48                         a[e.to] = min(a[x], e.cap - e.flow);
49                         Q.push(e.to);
50                     }
51                 }
52                 if (a[t]) break;
53             }
54             if (!a[t]) break;
55             for (int u = t; u != s; u = edges[p[u]].from) {
56                 edges[p[u]].flow += a[t];
57                 edges[p[u] ^ 1].flow -= a[t];
58             }
59             flow += a[t];
60         }
61         return flow;
62     }
63 };
64 
65 EdmondsKarp g;
66 vector<Edge> bak;
67 
68 int main() {
69     int n, m;
70     while (scanf("%d%d", &n, &m) == 2) {
71         g.init(n * 2);
72         for (int i = 0; i < n; i++) g.AddEdge(i, i + n, 1);
73         for (int i = 0, u, v; i < m; i++) {
74             scanf(" (%d,%d)", &u, &v);
75             g.AddEdge(u + n, v, INF);
76             g.AddEdge(v + n, u, INF);
77         }
78         int s = n, flow = n; bak = g.edges;
79         for (int i = 1; i < n; i++) {
80                 g.edges = bak;
81                 flow = min(flow, g.Maxflow(s, i));
82         }
83         printf("%d\n", flow);
84     }
85     return 0;
86 }