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[] x = new int[n];
		for(int i = 0; i < n; i++)
			x[i] = sc.nextInt();
		int answer = 1000000000;
		if(n == k) {
			answer = 0;
			if(x[0] < 0) {
				answer -= x[0]; 
				if(x[n-1] > 0)
					answer += x[n-1];
			}
			else
				answer += x[n-1];
		}
		else {
			int[] distance = new int[n-k];
			for(int i = 0; i < n-k; i++) {
				distance[i] = Math.abs(x[i+k-1]-x[i]);
				distance[i] += Math.min(Math.abs(x[i+k-1]), Math.abs(x[i]));
			}
			for(int i = 0; i < n-k; i++)
				answer = Math.min(answer, distance[i]);
		}
		System.out.println(answer);
	}

}