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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Diagnostics;
class P
{
    static void Main()
    {
        string[] s = Console.ReadLine().Split();
        int n, k;
        n = int.Parse(s[0]);
        k = int.Parse(s[1]);
        long[] x = Console.ReadLine().Split().Select(long.Parse).ToArray();
        long ans = long.MaxValue;
        List<long> left = new List<long>();
        List<long> right = new List<long>();
        foreach (var i in x)
        {
            if (i < 0)
                left.Add(i);
            if (i > 0)
                right.Add(i);
            if (i == 0)
                k--;
        }
        left.Reverse();
        long[] lefts = new long[left.Count + 1];
        long[] rights = new long[right.Count + 1];
        for (int i = 1; i <= left.Count; i++)
            lefts[i] = left[i - 1];
        for (int i = 1; i <= right.Count; i++)
            rights[i] = right[i - 1];
        for (int i = 0; i < k; i++)
        {
            try
            {
                long temp = rights[k - i] - 2 * lefts[i];
                Debug.WriteLine(temp);
                ans = Math.Min(ans, temp);
            }
            catch
            {  }
        }
        for (int i = 0; i < k; i++)
        {
            try
            {
                long temp = -lefts[k - i] + 2 * rights[i];
                Debug.WriteLine(temp);
                ans = Math.Min(ans, temp);
            }
            catch
            {  }
        }
        try
        {
            ans = Math.Min(ans, rights[k]);
        }
        catch
        { }
        try
        {
            ans = Math.Min(ans, -lefts[k]);
        }
        catch
        { }
        Console.WriteLine(ans);
    }
}