poj 3411 Paid Roads (dfs)

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdlib>
 4 #include <cmath>
 5 #include <cstdio>
 6 #include <vector>
 7 #include <algorithm>
 8 #define LL long long
 9 using namespace std;
10 const int maxn = 20+10;
11 const int INF = 1<<28;
12 int n, m, vis[maxn], ans;
13 struct node
14 {
15     int b, c, p, r;
16 }tmp;
17 vector<node>v[maxn];
18 
19 void dfs(int x, int cost)
20 {
21     vis[x] ++;
22     if(cost >= ans) return;
23     if(x == n)
24     {
25         ans = cost;
26         return;
27     }
28     int t, b1;
29     for(int i = 0; i < v[x].size(); i++)
30     {
31         b1 = v[x][i].b;
32         if(vis[b1]<=3)
33         {
34             t = INF;
35             if(vis[v[x][i].c])
36             t = v[x][i].p;
37             if(t > v[x][i].r)
38             t = v[x][i].r;
39             dfs(b1, cost+t);
40             vis[b1] --;
41         }
42     }
43 }
44 int main()
45 {
46     int i;
47     int a1, b1, c1, p1, r1;
48     while(~scanf("%d%d", &n, &m))
49     {
50         ans = INF;
51         memset(vis, 0, sizeof(vis));
52         for(i = 0; i < m; i++)
53         {
54           cin>>a1>>b1>>c1>>p1>>r1;
55           tmp.b = b1; tmp.c = c1;
56           tmp.p = p1; tmp.r = r1;
57           v[a1].push_back(tmp);
58         }
59         dfs(1, 0);
60         if(ans == INF) cout<<"impossible"<<endl;
61         else cout<<ans<<endl;
62     }
63     return 0;
64 }