A strange lift

---

title: A strange lift
tags: [广搜,最短路径]

题目链接

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 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

有一栋楼，它有电梯，但是每层楼只有两个按钮，UP 和down ，这层楼只能上x层或者下x层，层数大于等于1，当然小于楼层高度。

分析

简单的广搜问题，由于在最短路分类中找到的这个题目，就用对短路来做了。

代码

#include<bits/stdc++.h>
#define inf 0x3f3f3f3f
#define MAX1 1050
 int road[MAX1][MAX1];
using namespace std;
int dij(int n,int s,int e)
{
    int vis[n+1]= {0};
    int dis[n+1];
    for (int i=1; i<=n; i++)
        dis[i]=road[s][i];
    vis[s]=1;
    int count1=1;
    int op=s;
    while (count1<n)
    {
        int min1=inf;
        for (int i=1; i<=n; i++)
        {
            if (vis[i]==0&&dis[i]<min1)
            {
                min1=dis[i];
                op=i;
            }
        }
        vis[op]=1;
        count1++;
        for (int i=1; i<=n; i++)
        {
            if (vis[i]==0&&dis[i]>dis[op]+road[op][i])
                dis[i]=dis[op]+road[op][i];
        }
    }
    return dis[e];
}

int main()
{

    int n,a,b;
    while (scanf("%d",&n),n)
    {
        scanf("%d%d",&a,&b);
        int f[MAX1];

        for (int i=1; i<=n; i++)
            for (int j=1; j<=n; j++)
                if (i==j)road[i][j]=0;
                else road[i][j]=inf;
        for (int i=1; i<=n; i++)
        {
            int a;
            scanf("%d",&a);
            if (i-a>=1)
                road[i][i-a]=1;
            if (i+a<=n)
                road[i][i+a]=1;
        }
        int s=dij(n,a,b);
        if(s==inf)s=-1;
        printf("%d
",s);

    }

    return 0;
}
/**

*/