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)

#![allow(dead_code, unused_imports, non_snake_case)]

use std::io::*;
use std::cmp::{max, min, Ordering};
use std::collections::*;
use std::str::FromStr;

const MOD: i32 = 1_000_000_007;

fn main() {
    let (_, mut k): (usize, usize) = input();
    let t: Vec<i64> = input();
    let mut plus = Vec::new();
    let mut minus = Vec::new();
    for &x in &t {
        if x == 0 {
            k -= 1;
        } else if x < 0 {
            minus.push(x.abs() as usize);
        } else {
            plus.push(x.abs() as usize);
        }
    }
    plus.sort();
    minus.sort();
//    println!("{:?}", plus);
//    println!("{:?}", minus);

    if k == 0 {
        println!("0");
        return;
    }

    let mut ans: usize = 1 << 29;

    // 片方だけ
    if plus.len() >= k {
        ans = min(ans, plus[k-1]);
    }
    if minus.len() >= k {
        ans = min(ans, minus[k-1]);
    }

    // ターンする
    for i in 1..k {
        if i <= minus.len() && k-i <= plus.len() {
            ans = min(ans, minus[i-1]*2 + plus[k-i-1]);
        }
        if i <= plus.len() && k-i <= minus.len() {
            ans = min(ans, plus[i-1]*2 + minus[k-i-1]);
        }
    }
    println!("{}", ans);
}

trait Read {
    fn read(s: &str) -> Self;
}

fn input<T: Read>() -> T {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).unwrap();
    T::read(buf.trim_right())
}

macro_rules! read_impl {
    ($($t:ty)*) => ($(
        impl Read for $t {
            fn read(s: &str) -> $t{
                s.parse().unwrap()
            }
        }
    )*)
}
read_impl! { usize u8 u16 u32 u64 isize i8 i16 i32 i64 f32 f64 }

impl Read for String {
    fn read(s: &str) -> Self {
        s.to_string()
    }
}

impl Read for Vec<char> {
    fn read(s: &str) -> Self {
        s.chars().collect()
    }
}

impl<T: Read> Read for Vec<T> {
    fn read(s: &str) -> Self {
        s.split_whitespace().map(T::read).collect()
    }
}

impl<A: Read, B: Read> Read for (A, B) {
    fn read(s: &str) -> Self {
        let tokens: Vec<_> = s.split_whitespace().collect();
        (A::read(tokens[0]), B::read(tokens[1]))
    }
}

impl<A: Read, B: Read, C: Read> Read for (A, B, C) {
    fn read(s: &str) -> Self {
        let tokens: Vec<_> = s.split_whitespace().collect();
        (A::read(tokens[0]), B::read(tokens[1]), C::read(tokens[2]))
    }
}

impl<A: Read, B: Read, C: Read, D: Read> Read for (A, B, C, D) {
    fn read(s: &str) -> Self {
        let tokens: Vec<_> = s.split_whitespace().collect();
        (A::read(tokens[0]), B::read(tokens[1]), C::read(tokens[2]), D::read(tokens[3]))
    }
}