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: Accepted)

import java.util.Scanner


object Main {
  def main(args: Array[String]): Unit = {
    val sc = new Scanner(System.in)
    val n, k = sc.nextInt()
    val xs = new Array[Int](n)
    
    for (i <- xs.indices) {
      xs(i) = sc.nextInt()
    }
    
    var ans = 1000000000
    
    for (i <- 0 until n - k + 1) {
      val y = xs(i)
      val z = xs(i + k - 1)
      val distance = math.abs(z - y)
      if (math.min(y, z) > 0) {
        ans = math.min(ans, distance + math.min(y, z))
      } else if (math.max(y, z) < 0) {
        ans = math.min(ans, distance - math.max(y, z))
      } else {
        val m = math.min(math.abs(y), math.abs(z))
        ans = math.min(ans, distance + m)
      }
    }
    
    println(ans)
  }
  
  def printArray[T](arr: Array[T]): Unit = {
    for (i <- arr.indices) {
      print(s"${arr(i)} ")
    }
    println()
  }
}