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: Wrong Answer)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(System.out);
        String[] param = br.readLine().split(" ");
        int N = Integer.parseInt(param[0]);
        int K = Integer.parseInt(param[1]);

        String[] line = br.readLine().split(" ");
        List<Integer> list = new ArrayList<>();
        int minTime = 0;

        for (int i = 0; i < N; i++) {
            list.add(Integer.parseInt(line[i]));
        }

        for (int i = 0; i < N - (K - 1); i++) {
            int time = 0;
            int left = list.get(i);
            int right = list.get(i + (K - 1));

            if (left >= 0) { // 両方正
                time = right;
            } else if (right <= 0) { // 両方負
                time = left;
            } else { // rightが正、leftが負
                if (left * (-1) < right) {
                    time = left * (-2) + right;
                } else {
                    time = left * (-1) + right * 2;
                }
            }
            // out.println(time + ", " + minTime);
            if (minTime == 0 || time < minTime) {
                minTime = time;
            }
        }
        out.println(minTime);
        out.close();
    }
}