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)

object Main{
  def main(args: Array[String]): Unit = {
    //n <- 本数  k <- 火をつける数
    val Array(n, k) : Array[Int] = io.StdIn.readLine().split(' ').map(_.toInt)
    val candles = io.StdIn.readLine().split(' ').map(_.toInt)
    println(sunukeSetFire(n,k,candles))
  }

  /** 距離を計算する */
  def calcDistance(l:Int, r:Int) : Int = {
    if(l >= 0 && r >= 0) Math.max(l,r)
    else if(l <= 0 && r <= 0) Math.min(l,r).abs
    else if(l < r) (l*2).abs + r.abs
    else l.abs + (r*2).abs
  }

  /**
    * 0以上になるときのindexを返す
    * 0以上がないときは最後のindexを返す
    */
  def getFirstIndexGreaterThanZero(candle: Seq[Int]) ={
    candle.zipWithIndex.find(_._1 >=0).map(_._2).getOrElse(candle.length-1)
  }

  def sunukeSetFire(n:Int, k:Int, candles: Seq[Int]):Int ={
    var distances : List[Int] = Nil
    var index = (getFirstIndexGreaterThanZero(candles) - (k-1))
    val maxIndex = index + k + k
    index = index match {
      case num if(num >= 0) => num
      case _ => 0
    }

    //indexがリストの最大かmaxIndexになるまでループ
    while(index + k <= n && index + k <= maxIndex){
      val l = candles(index)
      val r = candles(index + k -1)
      println(s"l:${l} r:${r}   index: ${index}  maxindex: ${maxIndex}")
      distances = calcDistance(l,r) :: distances
      index += 1
    }
    distances.min
  }
}