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():
    num, walk_num = map(int, input().split())
    data_kari = list(map(int, input().split()))
    data = [0 for i in range(num)]

    for i in range(num):
        if data_kari[i] >= 0:
            break

    for j in range(i):
        if j == i - 1:
            data[j] = data_kari[j]
        else:
            data[j] = data_kari[j] - data_kari[j + 1]
    data[i] = data_kari[i]
    for j in range(i + 1, num):
        data[j] = data_kari[j] - data_kari[j -1]

    start_ind = max(0,i - walk_num + 1)

    data_sum_fu = 0
    data_sum_sei = 0

    for i in range(start_ind, start_ind + walk_num):
        if data[i] > 0:
            data_sum_sei += data[i]
        else:
            data_sum_fu += abs(data[i])
    ans = 2 * min(data_sum_sei, data_sum_fu) + max(data_sum_sei, data_sum_fu)


    for i in range(start_ind + 1, num - walk_num + 1):
        left_data = data[i - 1]
        right_data = data[i + walk_num - 1]

        if left_data > 0:
            break
        data_sum_fu -= abs(left_data)
        if right_data > 0:
            data_sum_sei += right_data
        else:
            data_sum_fu += abs(right_data)

        ans_kari = 2 * min(data_sum_sei, data_sum_fu) + max(data_sum_sei, data_sum_fu)

        if ans_kari < ans:
            ans = ans_kari

    print(ans)





if __name__ == '__main__':
    main()