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 Kotlin (1.3.71) (judge verdict: Accepted)

import kotlin.math.abs
import kotlin.math.min

fun intList() = readLine()?.split(" ")?.map(String::toInt) ?: TODO()
fun longList() = readLine()?.split(" ")?.map(String::toLong) ?: TODO()
fun main(args: Array<String>) {
    val (n, k) = intList()
    val x = longList()
    val b = (x.indexOfFirst { it >= 0 } + 1).takeIf { it > 0 } ?: n - 1
    var m = Long.MAX_VALUE
    ((b - k).takeIf { it > 0 } ?: 0).until(b + 1).forEach {
        if (it >= 0 && it + k <= n) {
            val l = x[it]
            val r = x[it + k - 1]
            m = if (l < 0) {
                if (r < 0) {
                    min(m, abs(l))
                } else {
                    min(m, min(abs(l) * 2 + r, abs(l) + r * 2))
                }
            } else {
                min(m, abs(r))
            }
        }
    }
    if (m == Long.MAX_VALUE) {
        println("0")
    } else {
        println(m.toString())
    }
}