HDU1548：A strange lift

　　　　　　　　　　　　　　HDU1548：A strange lift Dijkstra

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 are on floor A,and you want to go to floor B,how many times at least he has 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

 

题意：给出楼层数n，起始楼层和目的楼层；问最少经过几次的UP或者DOWN可以到达目的楼层

UP，会上升到i+k[i]层；DOWN会下降到i-k[i]层

所给数据中1-UP->4-UP->6超,回到4-DOWN->2-UP->5

有三步

 

#include<stdio.h>
#include<iostream>
#include<string.h>
#define max 0x3f3f3f3f

using namespace std;

int main()
{
    int n,a,b,x;
    int i,j,k,min;
    int floor[201][201],f[201],used[201];
    while(scanf("%d",&n)&&n)
    {

        memset(used,0,sizeof(used));
        scanf("%d %d",&a,&b);

        for(i=1;i<=n;i++)
        {
            for(j=1;j<=n;j++)
                floor[i][j]=max;

            scanf("%d",&x);///下面记录该楼层可到达的楼层，记为1
            if(i+x<=n)
                floor[i][i+x]=1;
            if(i-x>=1)
                floor[i][i-x]=1;
        }

        for(i=1;i<=n;i++)
            f[i]=floor[a][i];

        f[a]=0;//初值是起点到每个点的距离！

        for(i=1;i<=n;i++)
        {
            min=max;
            for(j=1;j<=n;j++)
                if(!used[j]&&f[j]<min)
                {
                    min=f[j];k=j;
                }

            if(min==max)
                break;
            used[k]=1;

            for(j=1;j<=n;j++)
                if(!used[j]&&f[j]>floor[k][j]+f[k])
                    f[j]=floor[k][j]+f[k];
        }

        if(f[b]==max)
            printf("-1
");
        else
            printf("%d
",f[b]);
    }
    return 0;
}