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.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		long[] x = new long[n + 1];
		long[] sum = new long[n + 1];
		sum[0] = 0;
		for(int i = 1; i < n + 1; i++) {
			x[i] = sc.nextLong();
			if(i == 1)
				sum[i] = 0;
			else {
				sum[i] = sum[i - 1] + x[i] - x[i - 1];
			}
		}
		long ans = Long.MAX_VALUE;
		for(int i = 1; k - 1 + i <= n; i++) {
			int tmp = k - 1 + i;
			long anstmp = 0;
			anstmp += sum[tmp] - sum[i];
			anstmp += Math.min(Math.abs(x[i]), Math.abs(x[tmp]));
			ans = Math.min(ans, anstmp);
		}
		System.out.println(ans);

	}

}