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: Runtime Error)

#coding:utf-8

n,k = map(int,input().split())
ls = list(map(int,input().split()))

# n, k = 5, 3
# ls = [-30,-10,10,20,50]

# n,k = 3,2
# ls=[10,20,30]

# n,k = 1,1
# ls = [0]

# n,k=8,5
# ls=[-9,-7,-4,-3,1,2,3,4]

def set_max(ls):
    try:
        return set([max(ls)])
    except:
        return set()
def set_min(ls):
    try:
        return set([min(ls)])
    except:
        return set()


plus = list(filter(lambda n:n>=0, ls))
minus = list(filter(lambda n:n<=0, ls))

neighbor = set_max(minus) | set_min(plus)

print (neighbor)
answer = []
for i in range(n-k+1):
    if len(set(ls[i:i+k])&neighbor)>0:
        print (ls[i:i+k])
        if sign(ls[i]*ls[i+k-1])<0:
            temp = [abs(ls[i]),abs(ls[i+k-1])]
            answer.append(2*min(temp)+max(temp))
        else:
            answer.append(2*max(temp))
print (min(answer))

# first = -1
# for i,point in enumerate(ls):
#     if point >= 0:
#         first = i
#         break
# size=k+1
# ans = []
# for i in range(size):
#     if first-size+i+1>=0 and first+i-1< len(ls):
#         temp = [0,ls[first-size+i+1],ls[first+i-1]]
#         temp = [abs(min(temp)),abs(max(temp))]
#         ans.append((2*min(temp)+max(temp)))
# print (min(ans))