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.ArrayList;

public class Main {

	public static void main(String[] args) throws NumberFormatException, IOException {

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

		String[] nk = br.readLine().split(" ");
		int n = Integer.parseInt(nk[0]);
		int k = Integer.parseInt(nk[1]);
		String[] xline = br.readLine().split(" ");

		ArrayList<Integer> list = new ArrayList<Integer>(k);
		int cur = Integer.parseInt(xline[0]);
		int min = 999999999;
		int kcopy = k;

		for (int i = 0; i < n; i++, kcopy--) {
			cur = Integer.parseInt(xline[i]);
			if (0 < kcopy) {
				list.add(cur);
				if (k == 1)
					min = Math.min(min, Math.abs(cur));
			} else {
				if (k == 1) {
					min = Math.min(min, Math.abs(cur));
				} else {
					int first = list.get(0);
					int last = list.get(list.size() - 1);
					if (Math.abs(first) < Math.abs(last)) {
						min = Math.min(min, Math.abs(first) + Math.abs(first - last));
					} else {
						min = Math.min(min, Math.abs(last) + Math.abs(first - last));
					}
				}
				list.remove(0);
				list.add(cur);
			}
		}

		System.out.println(min);

	}

}