codeforces - 500A 图的遍历 Java

A. New Year Transportation

time limit per test
 2 seconds

memory limit per test
 256 megabytes

input
 standard input

output
 standard output

New Year is coming in Line World! In this world, there are n cells numbered by integers from 1 to n,
as a 1 × n board. People live in cells. However, it was hard to move between distinct cells, because of the difficulty of escaping
the cell. People wanted to meet people who live in other cells.

So, user tncks0121 has made a transportation system to move between these cells, to celebrate the New Year. First, he thought of n - 1positive
integers a1, a2, ..., an - 1.
For every integer i where 1 ≤ i ≤ n - 1 the
condition 1 ≤ ai ≤ n - i holds.
Next, he made n - 1portals, numbered by integers from 1 to n - 1.
The i-th (1 ≤ i ≤ n - 1)
portal connects cell i and cell (i + ai),
and one can travel from cell i to cell (i + ai) using
the i-th portal. Unfortunately, one cannot use the portal backwards, which means one cannot move from cell(i + ai) to
cell i using the i-th
portal. It is easy to see that because of condition 1 ≤ ai ≤ n - i one
can't leave the Line World using portals.

Currently, I am standing at cell 1, and I want to Go to
cell t. However, I don't know whether it is possible to go there.
Please determine whether I can go to cell t by only using the construted transportation system.

Input

The first line contains two space-separated integers n (3 ≤ n ≤ 3 × 104)
and t (2 ≤ t ≤ n)
— the number of cells, and the index of the cell which I want to go to.

The second line contains n - 1 space-separated integers a1, a2, ..., an - 1 (1 ≤ ai ≤ n - i).
It is guaranteed, that using the given transportation system, one cannot leave the Line World.

Output

If I can go to cell t using the transportation system, print "YES".
Otherwise, print "NO".

Examples

input

8 4
1 2 1 2 1 2 1

output

YES

input

8 5
1 2 1 2 1 1 1

output

NO

import java.util.Scanner;

public class Main {

@SuppressWarnings("resource")
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
while (sc.hasNext()) {
int n = sc.nextInt();
int m = sc.nextInt();
int arr[] = new int[n ];
for (int i = 1; i < arr.length; i++) {
arr[i] = sc.nextInt();

}arr[0]=1;
int mix = 0;
for (int i = 0; i < arr.length; i=mix) {
if(mix>arr.length-1){break;}
if(arr[mix]==0){break;}

mix=arr[i]+mix;
if(mix==m){mix=Integer.MAX_VALUE;break;}

}
if (mix != Integer.MAX_VALUE) {
System.out.println("NO");
} else {
System.out.println("YES");
}

}
}

}