POJ 3411 Paid Roads(DFS)

题目链接

点和边 都很少，确定一个界限，爆搜即可。判断点到达注意一下，如果之前已经到了，就不用回溯了，如果之前没到过，要回溯。

 1 #include <cstring>
 2 #include <cstdio>
 3 #include <string>
 4 #include <iostream>
 5 #include <algorithm>
 6 #include <vector>
 7 #include <queue>
 8 using namespace std;
 9 struct node
10 {
11     int a,b,c,p,r,next;
12 } edge[101];
13 int first[21],t,minz;
14 int o[21],n;
15 void CL()
16 {
17     t = 1;
18     memset(first,-1,sizeof(first));
19     memset(o,0,sizeof(o));
20 }
21 void add(int a,int b,int c,int p,int r)
22 {
23     edge[t].a = a;
24     edge[t].b = b;
25     edge[t].c = c;
26     edge[t].p = p;
27     edge[t].r = r;
28     edge[t].next = first[a];
29     first[a] = t ++;
30 }
31 void dfs(int x,int sum)
32 {
33     int i,v,s,z;
34     if(sum >= minz)
35         return ;
36     if(x == n)
37     {
38         minz = min(sum,minz);
39         return ;
40     }
41     for(i = first[x]; i != -1; i = edge[i].next)
42     {
43         v = edge[i].b;
44         s = edge[i].c;
45         z = 0;
46         if(o[s])
47         {
48             if(o[v])
49             z = 1;
50             else
51             o[v] = 1;
52             dfs(v,sum+edge[i].p);
53             if(z == 0)
54             o[v] = 0;
55         }
56         else
57         {
58             if(o[v])
59             z = 1;
60             else
61             o[v] = 1;
62             dfs(v,sum+edge[i].r);
63             if(z == 0)
64             o[v] = 0;
65         }
66     }
67     return ;
68 }
69 int main()
70 {
71     int i,m,sum;
72     int a,b,c,p,r;
73     scanf("%d%d",&n,&m);
74     CL();
75     sum = 0;
76     for(i = 1; i <= m; i ++)
77     {
78         scanf("%d%d%d%d%d",&a,&b,&c,&p,&r);
79         add(a,b,c,p,r);
80         sum += r;
81     }
82     minz = sum+1;
83     o[1] = 1;
84     dfs(1,0);
85     if(minz == sum+1)
86         printf("impossible\n");
87     else
88         printf("%d\n",minz);
89     return 0;
90 }

 

posted @ 2013-07-06 15:31  Naix_x  阅读(189)  评论(0)  编辑  收藏  举报