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.util.*;

public class Main {

    public static void main(String[] args) {
        new Main().solve();
    }

    void solve() {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int K = sc.nextInt();
        int[] X = new int[N];
        int[] x = new int[N + 1];
        int All = Integer.MAX_VALUE;
        int s = 0;
        for (int i = 0; i < N; i++) {
            x[i] = sc.nextInt();
            if (x[s] <= 0 && Math.abs(x[s]) > Math.abs(x[i])) {
                s = i;
            }
        }
        if (s == 0) {
            System.out.println(x[s + (K - 1)]);
            return;
        }
        if (s == N - 1) {
            System.out.println(Math.abs(x[s - (K - 1)]));
            return;
        }
        int g;
        if (s + 1 - K > 0) {
            g = s - K;
        } else {
            g = 0;
        }
        for (int i = g; x[i] <= 0; i++) {
            if ((N - i) <= K) {
                break;
            }
            int c = Math.abs(x[i]);
            int n = K - (s - i);
            if (n != 0) {
                c += 2 * x[s + n];
            }
            All = Math.min(All, c);
        }
        if (N - 1 - s > K) {
            g = N - 1 - s;
        } else {
            g = N - 1;
        }
        for (int i = g; x[i] >= 0; i--) {
            if (i < K - 1) {
                break;
            }
            int c = x[i];
            int n = K - (i - s);
            if (n != 0) {
                c += 2 * Math.abs(x[s - (n - 1)]);
            }
            All = Math.min(All, c);
        }
        System.out.println(All);
    }
}