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 C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

int main(int argc, char const *argv[])
{
	long n, k, *x, ans, *r, *l, r1=1, l1=1, p=0;
	scanf("%ld%ld", &n, &k);
	x=(long *)malloc(sizeof(long)*n);
	r=(long *)malloc(sizeof(long)*(k+1));
	l=(long *)malloc(sizeof(long)*(k+1));
	for (int i = 0; i < n; ++i) scanf("%ld", &x[i]);
	while (x[p]<0) p++;
	r[0]=0;
	l[0]=0;
	for (int i = p; i < p+k; i++)
	{
		if (i>=n) break;
		r[r1]=x[i];
		r1++;
	}
	for (int i = 0; i < k; ++i)
	{
		if (p-1-i<0) break;
		l[l1]=-x[p-1-i];
		l1++;
	}
	ans=LONG_MAX;
	for (int i = 0; i <= k; ++i)
	{
		if (k-i<l1 && i<r1)
		{
			if (l[k-i]+2*r[i]<ans)
			{
				ans=l[k-i]+2*r[i];
			}
			if (2*l[k-i]+r[i]<ans)
			{
				ans=2*l[k-i]+r[i];
			}
		}

	}
	free(x);
	free(r);
	free(l);
	printf("%ld\n", ans);
	return 0;
}