[状压dp]POJ2686 Traveling by Stagecoach

 1 #include <cstdio>
 2 #include <cstdlib>
 3 #include <cstring>
 4 #include <climits>
 5 #include <cctype>
 6 #include <cmath>
 7 #include <string>
 8 #include <sstream>
 9 #include <iostream>
10 #include <algorithm>
11 #include <iomanip>
12 using namespace std;
13 #include <queue>
14 #include <stack>
15 #include <vector>
16 #include <deque>
17 #include <set>
18 #include <map>
19 typedef long long LL;
20 typedef long double LD;
21 #define INFF 0x3f3f3f3f
22 #define INF 2139062143
23 #define pi acos(-1.0)
24 #define lson l, m, rt<<1
25 #define rson m+1, r, rt<<1|1
26 typedef pair<int, int> PI;
27 typedef pair<int, PI> PP;
28 #ifdef _WIN32
29 #define LLD "%I64d"
30 #else
31 #define LLD "%lld"
32 #endif
33 //#pragma comment(linker, "/STACK:1024000000,1024000000")
34 //LL quick(LL a, LL b){LL ans=1;while(b){if(b & 1)ans*=a;a=a*a;b>>=1;}return ans;}
35 //inline int read(){char ch=‘ ‘;int ans=0;while(ch<‘0‘ || ch>‘9‘)ch=getchar();while(ch<=‘9‘ && ch>=‘0‘){ans=ans*10+ch-‘0‘;ch=getchar();}return ans;}
36 //inline void print(LL x){printf(LLD, x);puts("");}
37 //inline void read(int &x){char c = getchar();while(c < ‘0‘) c = getchar();x = c - ‘0‘; c = getchar();while(c >= ‘0‘){x = x * 10 + (c - ‘0‘); c = getchar();}}
38 
39 int t[15];
40 int mp[35][35];
41 double dp[1<<10][35];  // 剩下的车票状态  现在在v的最小花费
42 int main()
43 {
44 #ifndef ONLINE_JUDGE
45     freopen("in.txt", "r", stdin);
46     freopen("out.txt", "w", stdout);
47 #endif
48     int n, m, p, a, b;
49     while(~scanf("%d%d%d%d%d", &n, &m, &p, &a, &b) && (n || m || p || a || b))
50     {
51         for(int i=0;i<n;i++)
52             scanf("%d", &t[i]);
53         memset(mp, -1, sizeof(mp));
54         while(p--)
55         {
56             int u, v, w;
57             scanf("%d%d%d", &u, &v, &w);
58             u--, v--;
59             if(mp[u][v]<0)
60                 mp[u][v]=mp[v][u]=w;
61             else
62                 mp[u][v]=mp[v][u]=min(mp[u][v], w);
63         }
64         memset(dp, 127, sizeof(dp));
65         dp[(1<<n)-1][a-1]=0;
66         double ans=INF;
67         for(int s=(1<<n)-1;s>=0;s--)
68         {
69             ans=min(ans, dp[s][b-1]);
70             for(int v=0;v<m;v++)
71                 for(int i=0;i<n;i++)
72                     if(s>>i & 1)
73                         for(int u=0;u<m;u++)
74                             if(mp[v][u]>=0)
75                                 dp[s & ~(1<<i)][u]=min(dp[s & ~(1<<i)][u], dp[s][v]+mp[v][u]*1.0/t[i]);
76    // 使用车票i , v->u
77         }
78         if(ans==INF)
79             printf("Impossible\n");
80         else
81             printf("%.3lf\n", ans);
82     }
83     return 0;
84 }