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"
	"io"
	"os"
)

func main() {
	solve(os.Stdin, os.Stdout)
}

func solve(in io.Reader, out io.Writer) {
	var n, k int
	fmt.Fscanf(in, "%d%d", &n, &k)

	if n == 1 {
		var x0 int
		fmt.Fscan(in, &x0)
		fmt.Fprintln(out, x0)
		return
	}

	i0 := 0
	flg := true
	x := make([]int, n+1)
	for i := 0; i < n+1; i++ {
		fmt.Scan(&x[i])
		if x[i] > 0 && flg {
			x[i+1] = x[i]
			x[i] = 0
			i++
			i0 = i - 1
			flg = false
		}
	}

	// left to right
	lr := 0
	l, r := i0, i0
	for i := 0; i < k; i++ {
		costL := 1000000000
		costR := 1000000000
		if l > 0 {
			costL = 2 * (x[l] - x[l-1])
		}
		if r < n-1 {
			costR = x[r+1] - x[r]
		}
		if l > 0 && (r == n-1 || costL < costR) {
			lr += costL
			l--
		} else {
			lr += costR
			r++
		}
	}

	// right to left
	rl := 0
	l, r = i0, i0
	for i := 0; i < k; i++ {
		costL := 1000000000
		costR := 1000000000
		if l > 0 {
			costL = x[l] - x[l-1]
		}
		if r < n-1 {
			costR = 2 * (x[r+1] - x[r])
		}
		if l > 0 && (r == n-1 || costL < costR) {
			rl += costL
			l--
		} else {
			rl += costR
			r++
		}
	}

	if lr > rl {
		fmt.Fprintln(out, rl)
	} else {
		fmt.Fprintln(out, lr)
	}
}