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++14 (Clang 3.8.0) (judge verdict: Accepted)

#include <iostream>
#include <algorithm>
using namespace std;
#define MAX_N 100001

int N;
int K;
long int x[MAX_N];

int main(){
    cin >> N >> K;
    bool flag = true;
    for (int i = 0; i < N; i++){
        long int element;
        cin >> element;
        // if ((element > 0) && (flag)){
            // flag = false;
            // x[i] = 0;
            // i ++;
        // }
        x[i] = element;
    }
    // for (int i = 0; i <= N; i++){
    //     cout << x[i] << endl;
    // }
    int left = 0;
    int right = K - 1;
    long int distance = 10000000001;
    if (x[0] >= 0){
        distance = x[K - 1];
    }
    else if (x[N - 1] <= 0){
        distance = - x[N - K];
    }
    else{
        while (right < N){
            if ((x[right] >= 0) && (x[left] <= 0)){
                distance = min(min(2 * x[right] - x[left], x[right] - 2 * x[left]), distance);
            }
            left ++;
            right ++;
        }
    }
    cout << distance << endl;

    return 0;
}