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;
#define int long long
#define N 200100

int n,k,sz,sf,tmp,tt;
int a[N],b[N],c[N];
int ans=1e15;

signed main()
{
	scanf("%lld%lld",&n,&k);
	for (int i=1;i<=n;i++)
	{
		scanf("%lld",&a[i]);
		if (a[i]==0) tmp++;
		if (a[i]<0) b[++sf]=-a[i];
		if (a[i]>0) c[++sz]=a[i];
	}
	reverse(b+1,b+sf+1);
	if (tmp>=k) {puts("0"); return 0;}
	
	k-=tmp;
	if (sz>=k) ans=min(ans,c[k]);
	if (sf>=k) ans=min(ans,b[k]);
	
	for (int i=1;i<k;i++)
	{
		if (i>sz || k-i>sf) break;
		tt=min(c[i]*2+b[k-i],b[k-i]*2+c[i]);
		ans=min(ans,tt);
	}
	printf("%lld\n",ans);
	return 0;
}