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 <stdlib.h>
#include <stdbool.h>
#define ABS(a) ((a < 0)? -a : a)

void solve(int *x, int n, int K) {
    int i, ncur, pcur;
    int nmax = 0, pmax = 0, ncnt = 0, pcnt = 0;
    int ntmp, ptmp;
    bool nflg, pflg;
    for(i = 0; x[i] < 0; ++i);
    //printf("i: %d\n", i);
    ncur = i-1; pcur = i;
    while(ncnt + pcnt < K) {
        nflg = ncur >= 0;
        pflg = pcur < n;
        ntmp = (nflg)? x[ncur] : 0;
        ptmp = (pflg)? x[pcur] : 0;
        //printf("ncur: %d ntmp: %d pcur: %d ptmp: %d\n",ncur, ntmp, pcur, ptmp);
        if(nflg && pflg) {
            if(ABS(ntmp) < ptmp) { nmax = ntmp; --ncur; ++ncnt; }
            else                 { pmax = ptmp; ++pcur; ++pcnt; }
        } else if(nflg) {
            nmax = ntmp; --ncur; ++ncnt;
        } else if(pflg) {
            pmax = ptmp; ++pcur; ++pcnt;
        }
    }
    //printf("cnt: %d nmax: %d pmax: %d\n", ncnt+pcnt, nmax, pmax);
    printf("%d\n", (ABS(nmax) < pmax) ? ABS(nmax)*2 + pmax : ABS(nmax) + pmax*2);
}

int main(void)
{
    int N, K, i;
    scanf("%d %d", &N, &K);
    int *x = (int*)malloc((N+1)*sizeof(int));
    for(i = 0; i < N; ++i) { scanf("%d", &x[i]); }
    solve(x, N, K);
    return 0;
}