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.io.BufferedReader;
import java.io.InputStreamReader;

public class Main {

	static int N, K, Z = 0, F = 0;
	static int ANSWER = Integer.MAX_VALUE;
	static int[] DATA;

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] lineArr = br.readLine().split(" ");
		N = Integer.parseInt(lineArr[0]);
		K = Integer.parseInt(lineArr[1]);

		DATA = new int[N];

		lineArr = br.readLine().split(" ");

		int tmp;
		for (int i = 0; i < N; i++) {
			DATA[i] = Integer.parseInt(lineArr[i]);
			tmp = Integer.parseInt(lineArr[i]);

			if (tmp < 0) {
				F++;
			} else if (tmp == 0) {
				Z++;
			}

			DATA[i] = tmp;
		}

		int start = 0;
		if (F > K) {
			start = F - K + Z;
		}

		int startValue;
		int endValue;
		for (int i = start; i < N - K + 1; i++) {
			startValue = DATA[i];
			endValue = DATA[i + K - 1];

			tmp = endValue - startValue;
			tmp += Math.min(Math.abs(startValue), Math.abs(endValue));

			if (ANSWER > tmp) {
				ANSWER = tmp;
			}
		}

		System.out.println(ANSWER);

	}
}