Problem:
Score : 300 points

Problem Statement

There are N candles placed on a number line.
The i-th candle from the left is placed on coordinate x_i.
Here, x_1 < x_2 < ... < x_N holds.

Initially, no candles are burning.
Snuke decides to light K of the N candles.

Now, he is at coordinate 0.
He can move left and right along the line with speed 1.
He can also light a candle when he is at the same position as the candle, in negligible time.

Find the minimum time required to light K candles.

Constraints

1 \leq N \leq 10^5

1 \leq K \leq N

x_i is an integer.

|x_i| \leq 10^8

x_1 < x_2 < ... < x_N

Input

Input is given from Standard Input in the following format:

N K
x_1 x_2 ... x_N

Output

Print the minimum time required to light K candles.

Sample Input 1

5 3
-30 -10 10 20 50

Sample Output 1

40

He should move and light candles as follows:

Move from coordinate 0 to -10.

Light the second candle from the left.

Move from coordinate -10 to 10.

Light the third candle from the left.

Move from coordinate 10 to 20.

Light the fourth candle from the left.

Sample Input 2

3 2
10 20 30

Sample Output 2

20

Sample Input 3

1 1
0

Sample Output 3

0

There may be a candle placed at coordinate 0.

Sample Input 4

8 5
-9 -7 -4 -3 1 2 3 4

Sample Output 4

10

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int k=sc.nextInt();
        int[] ar=new int[n];
        int min=0;
        for(int i=0;i<n;i++){
            ar[i]=sc.nextInt();
            //min=Math.min(Math.abs(ar[i]-0),min);
        }
        int[] sum=new int[n];
        sum[0]=0;
        //System.out.println();
        for(int i=1;i<n;i++){
            sum[i]=ar[i]-ar[i-1]+sum[i-1];
            //System.out.print(sum[i]+" ");
        }
        int total=Integer.MAX_VALUE,x=-1;
        for(int i=0;i<=n-k;i++){
            int count=sum[i+k-1]-sum[i];
            //System.out.println("count="+count);
            if(total>count){
                total=count;
                x=i;
            }
        }
        /*if(ar[x]>=0 && ar[x+k-1]>=0){
            
        }
        else if(ar[x]<=0 && ar[x+k-1]<=0){
            
        }
        else{*/
            if(Math.abs(ar[x+k-1]-0)<Math.abs(ar[x]-0)){
                min=Math.abs(ar[x+k-1]-0);
            }
            else{
                min=Math.abs(ar[x]-0);
            }
        //}    
        total+=min;
        System.out.println(total);
    }  
}