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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;
public class Main {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		Main tr = new Main();
		tr.test(sc);
		sc.close();
	}
	
	void test(Scanner sc){
		int N = sc.nextInt();
		int K = sc.nextInt();
		int[] a = new int[N+1];
		a[1] = sc.nextInt();
		int here=-1;
		for (int i = 2; i <= N; i++) {
			a[i] = sc.nextInt();
			if(a[i-1]<= 0 && a[i] > 0){
				here = i;
			}
		}
		int out=0;
		if(here==-1){
			// all in one side
			if(a[1]>=0){
				out += a[K]; 
			}else{
				out += (-1 * a[N+1-K]);
			}
		}else{
			out  = Integer.MAX_VALUE;
			here--;
			int left = here>K?here-1-K:1;
			int right = left + K -1;
			here++;
			while(left<=here && right <= N){
				int dist = a[right]-a[left];
				int addme=0;
				if(a[left]<0){
					addme = (-1 * a[left]);
				}else{
					addme =a[left];
				}
				
				addme = addme>a[right]?a[right]:addme;
				
				dist+=addme;
				if(out>dist){
					out=dist;
				}
				left++;
				right++;
			}
		}
		System.out.println(out);
	}
}