poj 1724:ROADS（DFS + 剪枝）

 1 #include <iostream>
 2 #include <stdio.h>
 3 #include <string.h>
 4 using namespace std;
 5 
 6 #define MAXN 110
 7 
 8 struct Node{
 9     int city;
10     int len;
11     int toll;
12     Node* next;
13 }city[MAXN];    //邻接表
14 
15 bool isv[MAXN];
16 
17 int K,n,r,s;
18 int Min;
19 
20 void dfs(int c,int l,int k)
21 {
22     //k为剩下的钱
23     if(k<0)
24         return ;
25     if(l>=Min)    //如果当前走过的路的长度超过了记录的最小值，则退出
26         return ;
27     if(c==n && l<Min){    //到达n城市
28         Min = l;
29         return ;
30     }
31     
32     Node* p = city[c].next;
33     while(p){
34         if(!isv[p->city]){    //没走过 
35             isv[p->city] = true;
36             dfs(p->city,l + p->len,k - p->toll);    //进入下一个城市
37             isv[p->city] = false;
38         }
39         p = p->next;
40     }
41 }
42 
43 int main()
44 {
45     while(scanf("%d",&K)!=EOF){
46         scanf("%d",&n);
47         scanf("%d",&r);
48     
49         memset(city,NULL,sizeof(city));
50         memset(isv,0,sizeof(isv));
51         Min = 0x7ffffff;
52 
53         while(r--){
54             scanf("%d",&s);
55             Node* p = (Node*)malloc(sizeof(Node));
56             scanf("%d%d%d",&p->city,&p->len,&p->toll);
57             p->next = city[s].next;
58             city[s].next = p;
59         }
60 
61         isv[1] = true;
62         dfs(1,0,K);
63         
64         if(Min==0x7ffffff)
65             printf("-1\n");
66         else
67             printf("%d\n",Min);
68     }
69     return 0;
70 }