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.*;

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 ans = Integer.MAX_VALUE;

    // sacn minus range
    int i = K-1;
    if (x[0] < 0 && x[i] <= 0) {
      while (i < N && x[i] <= 0) {
        i++;
      }
      ans = Math.min(ans, Math.abs(x[i-K]));
    }
    
    // scan across zero range
    while (i < N && x[i-(K-1)] < 0) {
      int leftPos = Math.abs(x[i-(K-1)]);
      int rightPos = x[i];
      // turn left edge
      ans = Math.min(ans, 2*leftPos + rightPos);
      // turn right edge
      ans = Math.min(ans, leftPos + 2*rightPos);
      
      i++;
    }
    
    // scan plus range
    if (i < N && x[i-(K-1)] >= 0) {
      ans = Math.min(ans, x[i]);
    }
    
    System.out.println(ans);
  }
}