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(){
	long long N,K,min=9223372036854775807;
	scanf("%lld %lld",&N,&K);
	long long x[N];
	long long not_minus=N;
	int zero_exist=0;
	for(long long i=0;i<N;i++){
		scanf("%lld",&x[i]);
		if(not_minus==N && x[i]>=0)not_minus=i;
		if(x[i]==0)zero_exist=1;
	}
	
	if(zero_exist==1){
		if(N==1){
			printf("0\n");
			return 0;
		}
		N--;
		K--;
		for(long long i=not_minus;i<N;i++)x[i]=x[i+1];
	}
	
	if(K==1){
		if(not_minus==0)min=x[0];
		else if(not_minus==N)min=x[N-1]*(-1);
		else {
			min= x[not_minus-1]*(-1) < x[not_minus] ? x[not_minus-1]*(-1) : x[not_minus];
		}
		printf("%lld\n",min);
		return 0;
	}
	
	for(long long i=not_minus-K;i<=not_minus;i++){
		if(i<0 || i+K-1>=N)continue;
		int tmp=9223372036854775807;
		if(x[i]<0 && x[i+K-1]<0)tmp=x[i]*(-1);
		if(x[i]>0 && x[i+K-1]>0)tmp=x[i+K-1];
		else{
			if(x[i]*(-1)>x[i+K-1])tmp=x[i]*(-1)+x[i+K-1]*2;
			else tmp=x[i]*(-2)+x[i+K-1];
		}
		if(tmp<min)min=tmp;
	}
	
	printf("%lld\n",min);
	
	return 0;
}