HDOJ A strange lift

A strange lift

http://acm.hdu.edu.cn/diy/contest_showproblem.php?pid=1009&cid=12497&hide=0

Time Limit : 2000/1000ms (Java/Other)   Memory Limit : 65536/32768K (Java/Other)

Total Submission(s) : 5   Accepted Submission(s) : 2

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Problem Description

There is a strange lift.The lift can stop can at every floor as you want, and there is a number Ki(0 <= Ki <= N) on every floor.The lift have just two buttons: up and down.When you at floor i,if you press the button "UP" , you will go up Ki floor,i.e,you will go to the i+Ki th floor,as the same, if you press the button "DOWN" , you will go down Ki floor,i.e,you will go to the i-Ki th floor. Of course, the lift can't go up high than N,and can't go down lower than 1. For example, there is a buliding with 5 floors, and k1 = 3, k2 = 3,k3 = 1,k4 = 2, k5 = 5.Begining from the 1 st floor,you can press the button "UP", and you'll go up to the 4 th floor,and if you press the button "DOWN", the lift can't do it, because it can't go down to the -2 th floor,as you know ,the -2 th floor isn't exist.

Here comes the problem: when you is on floor A,and you want to go to floor B,how many times at least he havt to press the button "UP" or "DOWN"?

Input

The input consists of several test cases.,Each test case contains two lines.

The first line contains three integers N ,A,B( 1 <= N,A,B <= 200) which describe above,The second line consist N integers k1,k2,....kn.

A single 0 indicate the end of the input.

Output

For each case of the input output a interger, the least times you have to press the button when you on floor A,and you want to go to floor B.If you can't reach floor B,printf "-1".

Sample Input

5 1 5
3 3 1 2 5
0      

Sample Output

3

将其转化为图后又是最短路径水题，本人最喜欢做水题了，呵呵。

代码如下：

#include<iostream>

using namespace std;

const int maxnum=205;

const int maxint=9999999;

int map[maxnum][maxnum];

int dist[maxnum];

bool s[maxnum];

int n;

void Dijkstra(int v){

     for(int i=1;i<=n;i++){

         dist[i]=map[v][i];

         s[i]=0;

     }

     dist[v]=0;

     s[v]=1;

     for(int i=2;i<=n;i++){

          int temp=maxint;

          int u=v;

          for(int j=1;j<=n;j++)

                  if((!s[j]) && dist[j]<temp){ 

                      temp=dist[j];

                      u=j;

                  }

         // if(temp=maxint)  break; WA了N次，还不知道这一步为什么不能加额，哪位知道的请说一声     

         //当没找到相连的跳出没错啊，但结果纠结了 

          s[u]=1;

          for(int j=1;j<=n;j++)

               if((!s[j]) && dist[u]+map[u][j]<dist[j] )

                   dist[j]=dist[u]+map[u][j];                    

     } 

}

int main(){

    int a,b,x;

    while(scanf("%d",&n)!=EOF  && n ){

         scanf("%d%d",&a,&b);

         for(int i=1;i<=n;i++){

              for(int j=1;j<=n;j++)

                   map[i][j]=maxint;

              scanf("%d",&x);

              if(i+x<=n)

                  map[i][i+x]=1; //从第i楼到第i+x楼只需按一次就到达，所以令其边为1，下同

              if(i-x>=1)

                  map[i][i-x]=1;              

         }

         Dijkstra(a);

         if(dist[b]<maxint)

            printf("%d\n",dist[b]);

         else

            printf("-1\n");                                     

    }  

    return 0;

}