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 Scala (2.11.7) (judge verdict: Wrong Answer)

// C - Candles
// https://abc107.contest.atcoder.jp/tasks/arc101_a

import scala.io.StdIn.readLine

object Main extends App {

  val Array(n, k) = readLine.split(" ").map(_.toInt)
  val xs: Array[Int] = readLine.split(" ").map(_.toInt)

  val edges: List[(Int, Int)] = List.range(0, n-k).map(i => (xs(i), xs(i+k-1)))

  val lengths = edges.map(edge => {
    val left  = edge._1
    val right = edge._2
    val ltor = Math.abs(left)  + Math.abs(right - left)
    val rtol = Math.abs(right) + Math.abs(right - left)

    Math.min(ltor, rtol)
  })

  val length = if (lengths.length > 0) lengths.min else 0

  println(length)

}