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::cmp;
use std::collections::BinaryHeap;
use std::collections::HashMap;

fn read_line() -> String {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).ok();
    buf
}

fn main() {
    let nk: Vec<usize> = read_line().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nk[0];
    let k = nk[1];
    let xs: Vec<i32> = read_line().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let mid:Option<usize> = xs.iter().position(|&x| x >= 0);

    if mid.is_none() {
        println!("{}", -xs[n-k]);
    } else {
        let mid = mid.unwrap();

        let mut ans = xs[0].abs()*2 + xs[n-1].abs()*2;

        for i in 0..mid {
            if mid-i > k {
                ans = cmp::min(ans, xs[i].abs());
            } else if i+k-1 < n {
                ans = cmp::min(ans, xs[i].abs() + xs[i+k-1]*2);
                ans = cmp::min(ans, xs[i].abs()*2 + xs[i+k-1]);
            }
        }
        if mid+k-1 < n {
            ans = cmp::min(ans, xs[mid + k - 1]);
        }
        println!("{}", ans);
    }
}