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)

package com.sw;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

	private static int N;
	private static int K;
	private static int[] candle;;

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		N = Integer.parseInt(st.nextToken());
		K = Integer.parseInt(st.nextToken());
		candle = new int[N];
		st = new StringTokenizer(br.readLine());
		int index0 = 0;
		for (int i = 0; i < N; i++) {
			candle[i] = Integer.parseInt(st.nextToken());
			if(Math.abs(candle[i]) < Math.abs(candle[index0])){
				index0 = i;
			}
		}
		int minValue = Integer.MAX_VALUE;
		int begin = index0 - K + 1;
		int end = index0 + K - 1;
		if(candle[index0] < 0){
			end = index0 + K;
		}else{
			begin = index0 - K;
		}
		if(begin >= 0){
			minValue = Math.min(minValue, -candle[begin]);
			begin++;
		}else{
			begin = 0;
		}
		if(end < N){
			minValue = Math.min(minValue, candle[end]);
			end--;
		}else{
			end = N - 1;
		}
		for(int i = begin; i+K-1<=end; i++){
			minValue = Math.min(minValue, candle[i+K-1] - 2*candle[i]);
			minValue = Math.min(minValue, 2*candle[i+K-1] - candle[i]);
		}
		System.out.println(minValue);
	}
}