HDU 1548 A Strange Lift

Topic Connection

http://acm.hdu.edu.cn/showproblem.php?pid=1548

A Strange Liftdescription

There is a strange lift. The lift can stop can at every floor as you want, and there are a number $K _i (0 \leq k_i \leq N) $ on every floor. The lift has just, buttons:up, and down. When you are at floor i,if Press the button "up", you'll go up Ki floor,i.e,you'll go to the i+ki th floor,as the SAM E, if you press the button ' down ', you'll go down Ki floor,i.e,you'll go to the $i-k_i$ th floor. Of course, the lift can ' t go up high than $N $,and can ' t go down lower than 1. For example, there are a buliding with 5 floors, and $k _1 = 3, k_2 = 3,k_3 = 1,k_4 = 2, k_5 = 5$. Begining from the 1st Floor,you can press the button "up", and you'll go up to the 4th Floor,and if you press the button "Down", the lift can ' t do it, because it can ' t go down to the-2nd floor,as you know, the-2nd floor isn ' t exist.
Here comes the problem:when is on floor a,and you want to go to floor b,how many times at least he have to press the Button ' up ' or ' down '?

Input

The input consists of several test Cases.,each test case contains the lines.
The first line contains three integers $N, \ a,\ B (1 \leq n,a,b \leq) $ which describe above,the second line consist $N $ integers $k _1,k_2,.... k_n$.
A single 0 Indicate the end of the input.

Output

For each case of the input output a interger, the least times you had to press the button when you were on the floor a,and you wan T to go to floor b.if your can ' t reach floor b,printf "-1".

Sample Input

5 5 5
3 3 1) 2 5
0

Sample Output

3

Simple BFS ...

1#include <algorithm>2#include <iostream>3#include <cstdlib>4#include <cstring>5#include <cstdio>6#include <vector>7#include <queue>8#include <map>9 usingstd::cin;Ten usingstd::cout; One usingStd::endl; A usingStd::find; - usingStd::sort; - usingStd::map; the usingstd::p air; - usingstd::vector; - usingStd::queue; - #definePB (E) push_back (e) + #defineSZ (c) (int) (c). Size () - #defineMP (A, b) Make_pair (A, B) + #defineAll (c) (c). Begin (), (c). End () A #defineITER (c) Decltype ((c). Begin ()) at #defineCLS (arr,val) memset (arr,val,sizeof (arr)) - #defineCpresent (c, E) (Find (All (c), (e))! = (c). End ()) - #defineRep (i, n) for (int i = 0; i < (int) (n); i++) - #defineTR (c, I) for (ITER (c) i = (c). Begin (); I! = (c). end (); ++i) - Const intMax_n = About; - Const intDx[] = {-1,1 }; intypedef unsignedLong Longull; - BOOLVis[max_n]; to intN, A, B, arr[max_n]; + structNode { -     intx, S; theNode (inti =0,intj =0): X (i), S (j) {} * }; $ voidBFs () {Panax NotoginsengCLS (Vis,0); -Queue<node>que; theQue.push (Node (A),0)); +Vis[a] =true; A      while(!Que.empty ()) { theNode TP =Que.front (); Que.pop (); +         if(tp.x = = B) {printf ("%d\n", TP.S);return; } -Rep (I,2) { $             intNX = dx[i] * arr[tp.x] +tp.x; $             if(NX <0|| NX > N | | VIS[NX])Continue; -Que.push (The Node (NX, TP.S +1)); -VIS[NX] =true; the         } -     }WuyiPuts"-1"); the } - intMain () { Wu #ifdef LOCAL -Freopen ("In.txt","R", stdin); AboutFreopen ("OUT.txt","w+", stdout); $ #endif -      while(~SCANF ("%d", &n) &&N) { -scanf"%d%d", &a, &B); -Rep (i, N) scanf ("%d", &arr[i +1]); A BFS (); +     } the     return 0; -}

View Code

HDU 1548 A Strange Lift