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 (GCC 5.4.1) (judge verdict: Wrong Answer)


#include<stdio.h>
#include<math.h>
int min(int a, int b)
{
    if (a < b)
        return a;
    else
        return b;
}
int main()
{
    int n, k;
    scanf("%d %d", &n, &k);
    int x[100005];
    int i;
    for (i = 0; i < n; i++)
        scanf("%d", &x[i]);
    if (k == 1)
    {
        printf("%d\n", abs(x[0]));
        return 0;
    }
    int ans = 999999999;
    int t;
    for (i = 0; i < n - k; i++)
    {
        t = min(abs(x[i]), abs(x[i + k - 1]));
        t += x[i + k - 1] - x[i];
        ans = min(ans, t);
    }
    printf("%d\n", ans);
    return 0;
}