uva11600 状压期望dp

 1 #pragma warning(disable:4996)
 2 #pragma comment(linker, "/STACK:1024000000,1024000000")
 3 #include <stdio.h>
 4 #include <string.h>
 5 #include <time.h>
 6 #include <math.h>
 7 #include <map>
 8 #include <set>
 9 #include <queue>
10 #include <stack>
11 #include <vector>
12 #include <bitset>
13 #include <algorithm>
14 #include <iostream>
15 #include <string>
16 #include <functional>
17 const int INF = 1 << 30;
18 typedef __int64 LL;
19 /*
20 
21 */
22 const int N = 30 + 10;
23 std::vector<int> g[N];
24 std::map<int, double> dp[N];
25 int cnt[N];
26 int p, n;
27 bool vis[N];
28 int dfs(int u)
29 {
30     vis[u] = true;
31     int ret = 1;
32     for (int i = 0;i < g[u].size();++i)
33     {
34         int v = g[u][i];
35         if (vis[v]) continue;
36         ret += dfs(v);
37     }
38     return ret;
39 }
40 
41 double DP(int u, int s)
42 {
43     int have = 0;
44     if (dp[u].count(s)) return dp[u][s];
45     for (int i = 0;i < n;++i)
46         if (s&(1 << i))
47             have += cnt[i];
48     if (have == n) return 0;//dp[][n] 的期望是0
49     dp[u][s] = (n - 1)*1.0 / (n - have);
50     for (int i = 0;i < p;++i)
51     {
52         if (s&(1 << i)) continue;
53         dp[u][s] += DP(i, s|(1 << i)) * cnt[i] / (n - have);
54     }
55     return dp[u][s];
56 }
57 int main()
58 {
59     int t, m;
60     scanf("%d", &t);
61     for (int k = 1;k <= t;++k)
62     {
63         scanf("%d%d", &n, &m);
64         p = 0;
65         for (int i = 1;i <= n;++i)
66         {
67             g[i].clear();
68             vis[i] = 0;
69         }
70         int u, v;
71         for (int i = 0;i < m;++i)
72         {
73             scanf("%d%d", &u, &v);
74             g[u].push_back(v);
75             g[v].push_back(u);
76         }
77         for (int i = 1;i <= n;++i)
78             if (!vis[i])
79             {
80                 dp[p].clear();
81                 cnt[p++] = dfs(i);
82             }
83         
84         printf("Case %d: %.6lf\n",k, DP(0, 1));
85     }
86     return 0;
87 }