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<stdio.h>

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

  int x[N+1];
  for(int i=0;i<N;i++) scanf("%d",&x[i]);

  int min=100000000;
  for(int i=0;i<N-K+1;i++) {
    int xl,xr;
    xl = x[i];
    xr = x[i+K-1];
    if((xl*xr>=0)&&(xr<=0)) {
      if(-xl<min) min=-xl;
    }
    else if((xl*xr>=0)&&(xl>=0)) {
      if(xr<min) min=xr;
    }
    else {
      if(xr-2*xl>2*xr-xl) {
	if(2*xr-xl<min) min=2*xr-xl;
      }
      else {
	if(xr-2*xl<min) min=xr-2*xl;
      }
    }
  }
  printf("%d",min);
  return(0);
}