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)

// AtCoder My Practice
// author: Leonardone @ NEETSDKASU

fn main() {
	let mut stdin = String::new();
    std::io::Read::read_to_string(
    	&mut std::io::stdin(),
        &mut stdin).unwrap();
	let mut stdin = stdin.split_whitespace();
    let mut get = || stdin.next().unwrap();
    macro_rules! get {
    	($t:ty) => (get().parse::<$t>().unwrap());
        () => (get!(i64));
    }
    
    let n = get!(usize);
    let mut k = get!(usize);
    let mut xs = vec![];
    let mut ys = vec![];
    for _ in 0..n {
    	let x = get!();
        if x < 0 {
	        xs.push(x);
        } else if x > 0 {
        	ys.push(x);
        } else {
        	k -= 1;
        }
    }
    if k == 0 {
    	println!("0");
        return;
    }
    xs.reverse();
    if xs.len() == 0 {
    	println!("{}", ys[k - 1].abs());
        return;
    }
    if ys.len() == 0 {
    	println!("{}", xs[k - 1].abs());
        return;
    }
    let mut ans = std::i64::MAX;
    if k <= xs.len() {
    	ans = std::cmp::min(ans, xs[k - 1].abs());
    }
    if k <= ys.len() {
    	ans = std::cmp::min(ans, ys[k - 1].abs());
    }
    for i in 0..n {
    	let j = k - (i + 1) - 1;
        if i >= xs.len() || j >= ys.len() {
        	continue;
        }
        let tmp = xs[i].abs() * 2 + ys[j].abs();
        let tmp2 = xs[i].abs() + ys[j].abs() * 2;
        ans = std::cmp::min(ans, std::cmp::min(tmp, tmp2));
    }
    println!("{}", ans);
}