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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+7;
int pos[N],neg[N],a[N];
int n,k,p,az,x,y,ax;
int ans=2000000000;
int main(){
//	freopen("p.in","r",stdin);
	cin>>n>>k;
	for(int i=1;i<=n;i++){
	cin>>a[i];
	if(p==0&&a[i]>0)p=i;
	}
	int l=3;
	for(int i=p-1;i>0;i--)
	neg[p-i]=-1*a[i];
	for(int i=p;i<=n;i++)
	pos[i-p+1]=a[i];
	az=min(k,n-p+1);
	if(p!=0) ax=min(p-1,k);
	if(p==1)ax=0;
	ax=k-ax;
	if(p==0){az=0;ax=0;}
	for(int i=ax;i<=az;i++){
	 x=pos[i]; y=neg[k-i];
	ans=min(ans,2*x+y);
	ans=min(ans,x+2*y);
	}
	cout<<ans;
	return 0;
}