Problem:
Score : 500 points

Problem Statement

Given are N integers A_1,\ldots,A_N.

We will choose exactly K of these elements. Find the maximum possible product of the chosen elements.

Then, print the maximum product modulo (10^9+7), using an integer between 0 and 10^9+6 (inclusive).

Constraints

1 \leq K \leq N \leq 2\times 10^5

|A_i| \leq 10^9

Input

Input is given from Standard Input in the following format:

N K
A_1 \ldots A_N

Output

Print the maximum product modulo (10^9+7), using an integer between 0 and 10^9+6 (inclusive).

Sample Input 1

4 2
1 2 -3 -4

Sample Output 1

12

The possible products of the two chosen elements are 2, -3, -4, -6, -8, and 12, so the maximum product is 12.

Sample Input 2

4 3
-1 -2 -3 -4

Sample Output 2

1000000001

The possible products of the three chosen elements are -24, -12, -8, and -6, so the maximum product is -6.

We print this value modulo (10^9+7), that is, 1000000001.

Sample Input 3

2 1
-1 1000000000

Sample Output 3

1000000000

The possible products of the one chosen element are -1 and 1000000000, so the maximum product is 1000000000.

Sample Input 4

10 10
1000000000 100000000 10000000 1000000 100000 10000 1000 100 10 1

Sample Output 4

999983200

Be sure to print the product modulo (10^9+7).

Solution in Rust (1.42.0) (judge verdict: Accepted)

// This code is generated by [cargo-atcoder](https://github.com/tanakh/cargo-atcoder)
// Original source code:
/*
use competitive::prelude::*;

type GF = competitive::gf::GF<promote!(1_000_000_007)>;

fn main() {
    input! {
        n: usize,
        k: usize,
        mut a: [i64; n],
    }

    let ans = if n == k {
        let mut ans = GF::new(1);
        for i in 0..n {
            ans *= a[i];
        }
        ans
    } else if a.iter().all(|r| *r <= 0) {
        a.sort();
        if k % 2 == 1 {
            a.reverse();
        }
        let mut ans = GF::new(1);
        for a in a[0..k].iter() {
            ans *= *a;
        }
        ans
    } else {
        let mut ns = a.iter().filter(|r| **r < 0).cloned().collect_vec();
        let mut ps = a.iter().filter(|r| **r >= 0).cloned().collect_vec();

        ns.sort();
        ps.sort();
        ps.reverse();

        let mut i = min(k / 2 * 2, ns.len() / 2 * 2);
        let mut j = k - i;

        while i > 0 && i - 2 + ps.len() >= k && ns[i - 2] * ns[i - 1] < ps[j] * ps[j + 1] {
            i -= 2;
            j += 2;
        }

        let mut ans = GF::new(1);

        for a in ns[0..i].iter() {
            ans *= *a;
        }
        for a in ps[0..j].iter() {
            ans *= *a;
        }

        ans
    };

    echo!(ans);
}
*/

fn main() {
    let exe = "/tmp/bin2B9D77C0";
    std::io::Write::write_all(&mut std::fs::File::create(exe).unwrap(), &decode(BIN)).unwrap();
    std::fs::set_permissions(exe, std::os::unix::fs::PermissionsExt::from_mode(0o755)).unwrap();
    std::process::exit(std::process::Command::new(exe).status().unwrap().code().unwrap())
}

fn decode(v: &str) -> Vec<u8> {
    let mut ret = vec![];
    let mut buf = 0;
    let mut tbl = vec![64; 256];
    for i in 0..64 { tbl[TBL[i] as usize] = i as u8; }
    for (i, c) in v.bytes().filter_map(|c| { let c = tbl[c as usize]; if c < 64 { Some(c) } else { None } }).enumerate() {
        match i % 4 {
            0 => buf = c << 2,
            1 => { ret.push(buf | c >> 4); buf = c << 4; }
            2 => { ret.push(buf | c >> 2); buf = c << 6; }
            3 => ret.push(buf | c),
            _ => unreachable!(),
        }
    }
    ret
}

const TBL: &'static [u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const BIN: &'static str = "<base64-encoded ELF executable removed>";