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: Runtime Error)

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {
	static boolean[] visited ;
	static int[] point;
	static int stepNum;
	static int result = Integer.MAX_VALUE; 
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int num = sc.nextInt();
		stepNum = sc.nextInt();
		point = new int[num+1];
		boolean flag = true;
		int start = -1;
		
		visited = new boolean[point.length];
		
		for(int i = 0 ; i < point.length; i++){
			int temp = sc.nextInt();
			if(temp >= 0 && flag){
				point[i] = 0;
				start = i;
				i++;
				flag = false;
			}
			point[i] = temp;
		}
		visited[start] = true;
		
		findMinDis(0,start,0);
		System.out.println(result);
	}
	
	public static void findMinDis(int dist, int start, int step) {
		
		List<Integer> adj = findAdj(start);
		
		if(step == stepNum) {
			if (result > dist) {
				result = dist;
			}
			return;
		}
		
		for(int i = 0; i < adj.size(); i++){
			dist +=  Math.abs(adj.get(i)-point[start]);
			step++;
			int index = findIndex(adj.get(i));
			visited[index] = true;
			findMinDis(dist, index, step);
			dist -=  Math.abs(adj.get(i)-point[start]);
			step--;
			visited[index] = false;
		}
		
	}
	
	public static List<Integer> findAdj(int Strat) {
		List<Integer> list = new ArrayList<Integer>();
		for(int j = Strat; j >= 0 ; j--){
			if(!visited[j]){
				list.add(point[j]);
				break;
			}
		}
		for(int j = Strat+1; j < point.length ; j++){
			if(!visited[j]){
				list.add(point[j]);
				break;
			}
		}
		return list;
	}
	
	public static int findIndex(int val){
		for(int i = 0; i < point.length; i++) {
			if(val == point[i]) {
				return i;
			}
		}
		return -1;
	}
	
}