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::cmp;
use std::io;
use std::io::{BufRead, Write};

fn solve<R: BufRead, W: Write>(mut input: R, mut output: W) {
    let mut buf = String::new();
    input.read_line(&mut buf).unwrap();
    let (n, k): (usize, usize) = {
        let mut split = buf.split_whitespace();
        (
            split.next().unwrap().parse().unwrap(),
            split.next().unwrap().parse().unwrap(),
        )
    };
    buf.clear();
    input.read_line(&mut buf).unwrap();
    let x: Vec<i64> = buf.split_whitespace().map(|x| x.parse().unwrap()).collect();
    assert!(n == x.len());
    let zero_point = x.iter().position(|&x| x > 0).unwrap_or(x.len());
    let result = (0..k + 1)
        .flat_map(|i| {
            if i <= zero_point && zero_point + k - i - 1 < x.len() {
                let a = -cmp::min(x[zero_point - i], 0);
                let b = cmp::max(0, x[zero_point + k - i - 1]);
                vec![a * 2 + b, a + b * 2]
            } else {
                vec![]
            }
        })
        .min()
        .unwrap();
    writeln!(output, "{}", result).unwrap();
}

fn main() {
    let stdin = io::stdin();
    let stdout = io::stdout();
    solve(stdin.lock(), stdout.lock());
}

#[cfg(test)]
mod tests {
    fn test(input: &str, output: &str) {
        let mut v: Vec<u8> = Vec::new();
        ::solve(input.as_bytes(), &mut v);
        assert_eq!(String::from_utf8(v).unwrap(), output);
    }

    #[test]
    fn case1() {
        test(
            "5 3
-30 -10 10 20 50
",
            "40\n",
        );
    }

    #[test]
    fn case2() {
        test(
            "3 2
10 20 30
",
            "20\n",
        );
    }

    #[test]
    fn case3() {
        test(
            "1 1
0
", "0\n",
        );
    }
    #[test]
    fn case4() {
        test(
            "8 5
-9 -7 -4 -3 1 2 3 4
",
            "10\n",
        );
    }
}