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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>

int main (void)
{
    int N, K, x[100000] = {0};
    int i, pos0 = -1, posp, posn;

    scanf("%d %d", &N, &K);
    for (i = 0; i < N; i++) {
        scanf("%d", &x[i]);
        if (x[i] >= 0 && pos0 < 0) pos0 = i;
    }
    if (pos0 < 0) pos0 = i;

    if (pos0 == i || pos0 == 0) {
        if (pos0 == i) {
            printf("%d\n", -x[i - (K - 1)]);
            return 0;
        } else {
            printf("%d\n", x[(K - 1)]);
            return 0;
        }
    }

    if (x[pos0] > -x[pos0 - 1]) pos0 -= 1;
    posn = posp = pos0;

    while (1) {
        if ((posp - posn + 1) >= K) break;

        if (x[posp + 1] > -x[posn - 1]) posn -= 1;
        else  posp += 1;
    }

    if (x[posp] > -x[posn]) {
        printf("%d\n", -x[posn] * 2 + x[posp]);
    } else {
        printf("%d\n", x[posp] * 2 + -x[posn]);
    }

    return 0;
}