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: Wrong Answer)

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

int main()
{
  int N, K;
  scanf("%d %d", &N, &K);

  int array[N];
  int copy[N];

  for (int i = 0; i < N; i++)
    scanf("%d", &array[i]);

  int idx = 0;
  int i = N - 1;

  while (i >= 0)
  {
    copy[i] = array[i] - array[i - 1];
    if (array[i] > 0 && array[i - 1] < 0)
    {
      copy[i - 1] = -array[i - 1];
      i = i - 2;
    }
    i--;
  }

  int j = 0;
  if (array[0] < 0)
  {
    while (j < N)
    {

      if (array[j + 1] > 0)
        break;
      copy[j] = abs(array[j] - array[j + 1]);
      j++;
    }
  }

  int min = INT_MAX;
  int sum = 0;
  for (int i = 0; i < N; i++)
  {
    if (i + K >= N)
    {
      if (min == INT_MAX)min=0;
      break;
    } 
    for (int j = i; j < K+i; j++)
    {
      sum += copy[j];
    }
    
    if (sum < min)
      min = sum;
    sum = 0;
  }

  printf("%d", min);

  return 0;
}