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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;
use std::str::FromStr;
use std::cmp;

fn input_int_tuple() -> (i32, i32) {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    let vec: Vec<i32> = line.split_whitespace().map(|s| s.parse().unwrap()).collect();
    (vec[0], vec[1])
}

fn input_i32_vec() -> Vec<i32> {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    line.split_whitespace().map(|s| s.parse().unwrap()).collect()
}

fn main() {
    let (n, k) = input_int_tuple();
    let x_vec = input_i32_vec();
    if k == 1 {
        println!("{}", x_vec[0]);
        return;
    }
    let mut min = 1000000000u64;
    for i in 0..((n-k + 1) as usize) {
        let mut len = 0;
        // println!("{}, {}", x_vec[i], x_vec[i + k as usize - 1]);
        if (x_vec[i] <= 0 && x_vec[i + k as usize - 1] <= 0) || (x_vec[i] >= 0 &&(x_vec[i + k as usize - 1] >= 0)) {
            len += cmp::max(x_vec[i].abs(), x_vec[i + k as usize - 1].abs());            
        } else {            
            len += cmp::min(x_vec[i].abs(), x_vec[i + k as usize - 1].abs());
            // print!("{} ", len);
            len += x_vec[i + k as usize - 1] - x_vec[i];
            // println!("{}", len);
        }
        // println!("{}", len);
        if (len as u64) < min {
            min = len as u64;
        }
    }
    println!("{}", min);
}