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 Python (3.4.3) (judge verdict: Wrong Answer)

def main():
    N, K = list(map(int, input().split()))
    xs = list(map(int, input().split()))
    if 0 in xs:
        K = K - 1
    if K == 0:
        print(0)
        return

    posi = [x for x in xs if x > 0]
    nega = [x for x in xs if x < 0]

    min_total = 10 ** 8
    # print('nega: {}, posi:{}'.format(len(nega), len(posi)))
    if len(nega) == 0:
        print(posi[K-1])
        return
    if len(posi) == 0:
        print(nega[-K])
        return

    if len(nega) <= len(posi):
        for i in range(0, len(nega)+1):
            k = K
            k = k - i
            # print('i = {}, k = {}'.format(i, k))
            if i!= 0:
                total_dis = abs(nega[-i])
            else:
                total_dis = 0
            # print('only nega dis = {}'.format(total_dis))
            if k <= 0:
                continue
            use_posi = posi[:k]
            # print('use positive ={}'.format(use_posi))
            if i!=0:
                total_dis += abs(nega[-i]) + use_posi[-1]
            else:
                total_dis = use_posi[-1]
            # print('dis = {}'.format(total_dis))
            if total_dis < min_total:
                min_total = total_dis
    else:
        for i in range(1, len(posi)+1):
            k = K
            k = k - i
            total_dis = posi[-i]
            if k <= 0:
                continue
            use_nega = [nega[-i] for i in range(1, k+1)]
            total_dis += posi[-i] + abs(use_nega[0])
            if total_dis < min_total:
                min_total = total_dis
    print(min_total)

if __name__ == '__main__':
    main()