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: Accepted)

import java.util.*;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int K = sc.nextInt();

        int[] candles = new int[N];
        for (int i = 0; i < N; i++) {
            candles[i] = sc.nextInt();
        }

        int numWindows = N - K + 1;

        int minDist = -1;
        for (int i = 0; i < numWindows; i++) {
            int min = candles[i];
            int max = candles[i + K - 1];

            int dist = -1;
            if ((min < 0) && (max < 0)) {
                dist = -min;
            } else if ((min >= 0) && (max >= 0)) {
                dist = max;
            } else {
                if (max > -min) {
                    dist = max - min * 2;
                } else {
                    dist = max * 2 - min;
                }
            }

            if ((minDist == -1) || (dist < minDist)) {
                minDist = dist;
            }

        }

        System.out.println(minDist);
    }
}