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 scala.io.StdIn._
import java.lang.Math._
object Main {
  def main(args: Array[String]): Unit = {
    val NK = readLine.split("\\s+").toSeq.map{_.toInt}
    val N = NK(0)
    val K = NK(1)
    val x = readLine.split("\\s+").toSeq.map{_.toInt}
    val xs = for(i <- 0 to N - 1) yield x(i)
    val lb = scala.collection.mutable.ListBuffer[Int]()
    for(st <- 0 to N - K){
      if(xs(st) >= 0) lb += xs(st + K - 1)
      else if(xs(st + K - 1) > 0){
        lb += abs(xs(st))*2 + xs(st + K - 1)
        lb += xs(st + K - 1)*2 + abs(xs(st))
      }else lb += abs(xs(st))
    }
    println(lb.min.toString)
  }
}