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 (
	"bufio"
	"fmt"
	"math"
	"os"
)

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)

	var N, K int
	scanner.Scan()
	fmt.Sscanf(scanner.Text(), "%d", &N)
	scanner.Scan()
	fmt.Sscanf(scanner.Text(), "%d", &K)

	xs := make([]int, N)
	for i := 0; i < N; i++ {
		scanner.Scan()
		fmt.Sscanf(scanner.Text(), "%d", &xs[i])
	}

	fstPosIndex := -1
	for i := 0; i < len(xs); i++ {
		if xs[i] > 0 {
			fstPosIndex = i
			break
		}
	}

	left := max(fstPosIndex-K, 0)
	right := min(fstPosIndex+K-1, N-1)

	ans := math.MaxInt64
	for i := left; i+K-1 <= right; i++ {
		cost := 0

		if xs[i+K-1] < 0 {
			cost = abs(xs[i])
		} else if xs[i] > 0 {
			cost = abs(xs[i+K-1])
		} else {
			cost = min(2*abs(xs[i])+abs(xs[i+K-1]),
				abs(xs[i])+2*abs(xs[i+K-1]))
		}
		// fmt.Print(i, i+K-1)
		// fmt.Println(" => cost", cost)
		ans = min(ans, cost)
	}

	fmt.Println(ans)

}

func min(ns ...int) int {
	ret := math.MaxInt64
	for _, n := range ns {
		if n < ret {
			ret = n
		}
	}
	return ret
}

func max(ns ...int) int {
	ret := math.MinInt64
	for _, n := range ns {
		if n > ret {
			ret = n
		}
	}
	return ret
}

func abs(n int) int {
	if n >= 0 {
		return n
	}
	return -n
}