hdu1548 A strange lift(bfs 或Dijkstra最短路径)

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<cstring>
 5 #define M 205
 6 #define INF 0x3f3f3f3f
 7 using namespace std;
 8 
 9 int map[M][M];
10 int d[M], vis[M];
11 int n;
12 int b, e;
13 
14 void Dijkstra(){
15    memset(d, 0x3f, sizeof(d));
16    memset(vis, 0, sizeof(vis));
17    d[b]=0;
18    vis[b]=1;
19    int root=b;
20    for(int j=1; j<n; ++j){
21        int minLen=INF, p;    
22        for(int i=1; i<=n; ++i){
23           if(!vis[i] && d[i] > d[root] + map[root][i])
24               d[i] = d[root] + map[root][i];        
25           if(!vis[i] && minLen>d[i]){
26              p=i;
27              minLen=d[i];           
28           }
29        }
30        if(minLen==INF)
31           return;
32        root=p;
33        vis[root]=1;
34    }     
35 }
36 
37 int main(){
38    while(cin>>n && n){
39        cin>>b>>e;
40        memset(map, 0x3f, sizeof(map));
41        for(int i=1; i<=n; ++i){
42           int x, xx;
43           cin>>x;
44           map[i][i]=0;// i+(-)x 表示 从第i层可以到达第 i+（-）x层 
45           xx=i-x;
46           if(xx>=1) map[i][xx]=1;
47           xx=i+x;
48           if(xx<=n)  map[i][xx]=1;      
49        }             
50        Dijkstra();
51        if(d[e]==INF)
52           cout<<"-1"<<endl;
53        else
54           cout<<d[e]<<endl;
55    }
56    return 0;
57 } 

 1 /*
 2 思路：当前电梯位置的两个方向进行搜索！ 
 3       注意：搜索时的界限, 用x表示将要到达的电梯的位置 
 4             1. 首先是x>=1 
 5             2. x<=n
 6             3. vis[x]!=0 表明bfs时候没有经过这个楼层 
 7 */
 8 #include<iostream>
 9 #include<cstring>
10 #include<cstdio>
11 #include<queue> 
12 using namespace std;
13 struct node{
14    int x;
15    int step;       
16    node(){}
17    node(int x, int step){
18       this->x=x;
19       this->step=step;         
20    }
21 };
22 queue<node>q;
23 int n, b, e;
24 int f[205];
25 int vis[205];
26 
27 bool bfs(){
28     while(!q.empty())  q.pop();
29     memset(vis, 0, sizeof(vis)); 
30     q.push(node(b,0));
31     vis[b]=1;
32     while(!q.empty()){
33         node cur=q.front();
34         q.pop();
35         if(cur.x==e){
36             cout<<cur.step<<endl;
37             return true;             
38         }               
39         int xx;
40         xx=cur.x+f[cur.x];
41         if(xx==e){
42            cout<<cur.step+1<<endl;
43            return true;
44         }
45         if(xx<=n && !vis[xx]){
46            q.push(node(xx, cur.step+1));
47            vis[xx]=1;
48         }
49         xx=cur.x-f[cur.x];
50         if(xx==e){
51            cout<<cur.step+1<<endl;
52            return true;
53         }
54         if(xx>=1 && !vis[xx]){
55            q.push(node(xx, cur.step+1));
56            vis[xx]=1;
57         }
58     }
59     return false;
60 }
61       
62 int main(){
63     while(cin>>n && n){
64        cin>>b>>e;
65        for(int i=1; i<=n; ++i)
66           cin>>f[i];
67        if(!bfs())
68           cout<<"-1"<<endl;            
69     }
70     return 0;    
71 }