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 Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"fmt"
	"sort"
)

func getAbs(a int) int {
	if a < 0 {
		return a * -1
	}
	return a
}

func findMax(vec []int) (int, int) {
	pos := 0
	max := -2147483648
	for i, n := range vec {
		if max < n {
			pos = i
			max = n
		}
	}
	return pos, max
}

func findMin(vec []int) (int, int) {
	pos := 0
	min := 2147483647
	for i, n := range vec {
		if min > n {
			pos = i
			min = n
		}
	}
	return pos, min
}

type posSlice []int

func (p posSlice) Len() int {
	return len(p)
}
func (p posSlice) Swap(i, j int) {
	p[i], p[j] = p[j], p[i]
}
func (p posSlice) Less(i, j int) bool {
	return getAbs(p[i]) < getAbs(p[j])
}

func main() {
	var N, K int
	fmt.Scan(&N, &K)

	X := make(posSlice, N)
	for i := 0; i < N; i++ {
		fmt.Scan(&X[i])
	}

	sort.Sort(X)
	X = X[:K]

	_, max := findMax([]int(X))
	_, min := findMin([]int(X))

	if min >= 0 && max >= 0 {
		fmt.Println(max)
	} else if min < 0 && max < 0 {
		fmt.Println(-min)
	} else if getAbs(min) < getAbs(max) {
		fmt.Println(getAbs(min)*2 + max)
	} else {
		fmt.Println(getAbs(min) + max*2)
	}
}