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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        try {
            StringTokenizer st = new StringTokenizer(br.readLine());
            int N = Integer.valueOf(st.nextToken());
            int M = Integer.valueOf(st.nextToken());
            st = new StringTokenizer(br.readLine());
            int len=Integer.MAX_VALUE;
            int[] data=new int[N]; 
            for (int i = 0; i < N; i++) {
                int point = Integer.valueOf(st.nextToken());
                data[i]=point;
            }
            
            for (int i = 0; i < N-M+1; i++) {
                if(data[i]<0){
                    if(data[i+M-1]<0){
                        len=Math.min(len,Math.abs(data[i]));
                    }else if(data[i+M-1]==0){
                        len=Math.min(len,Math.abs(data[i]));
                    }else {
                        len=Math.min(len,Math.abs(data[i])*2+data[i+M-1]);
                        len=Math.min(len,Math.abs(data[i])+data[i+M-1]*2);
                    }
                }else if(data[i]==0){
                    len=Math.min(len,data[i+M-1]);
                }else{
                    len=Math.min(len,data[i+M-1]);
                }
            }
            if(N==M){
                if(N==1){
                    len=Math.min(len,Math.abs(data[0]));
                }else{
                    len=Math.min(len,Math.abs(data[0])*2+data[M-1]);
                    len=Math.min(len,Math.abs(data[0])+data[M-1]*2);
                }
            }
            System.out.println(len);
            
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

}