Kolakoski sequence: Difference between revisions

=={{header|Rust}}==

<lang rust>

use itertools::Itertools;

fn get_kolakoski_sequence(iseq: &[usize], size: &usize) -> Vec<usize> {

assert!(*size > 0);

assert!(!iseq.is_empty());

let mut kseq: Vec<usize> = Vec::default();

// create an itertor which keeps repeating the initial sequence infinitely

let repeater = iseq.iter().cloned().cycle();

// push the very first element, repeated as many times as the number

kseq.extend_from_slice(&vec![*iseq.get(0).unwrap()].repeat(*iseq.get(0).unwrap()));

//start cycling throught the initial sequence, but skip the very first one

for (k_counter, elem) in repeater.enumerate().skip(1) {

// push the given element

kseq.push(elem);

// and repeat the current element as many times

// as it's needed based on the previous elements

kseq.extend_from_slice(&vec![elem].repeat(*kseq.get(k_counter).unwrap() - 1));

// finish generation when the Kolakoski sequence has reached the given length

if kseq.len() >= *size {

break;

}

}

// truncate it as it might have more elements than needed

kseq[0..*size].to_vec()

}

fn is_kolakoski(kseq: &[usize]) -> bool {

assert!(!kseq.is_empty());

// calculate the RLE

let rle: Vec<usize> = kseq

.iter()

.batching(|it| {

it.next()

.map(|v| it.take_while_ref(|&v2| v2 == v).count() + 1)

})

.collect();

rle.iter().zip(kseq).filter(|&(a, b)| a == b).count() == rle.len()

}

fn main() {

let lengths = vec![20, 20, 30, 30];

let seqs = vec![vec![1, 2], vec![2, 1], vec![1, 3, 1, 2], vec![1, 3, 2, 1]];

for (seq, length) in seqs.iter().zip(&lengths) {

let kseq = get_kolakoski_sequence(&seq, length);

println!("Starting sequence: {:?}", seq);

println!("Kolakoski sequence: {:?}", kseq);

println!("Possible Kolakoski sequence? {:?}", is_kolakoski(&kseq));

}

}

</lang>

{{out}}

<pre>

Starting sequence: [1, 2]

Kolakoski sequence: [1, 2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1]

Possible Kolakoski sequence? true

Starting sequence: [2, 1]

Kolakoski sequence: [2, 2, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 2, 1, 1, 2, 2, 1, 2]

Possible Kolakoski sequence? true

Starting sequence: [1, 3, 1, 2]

Kolakoski sequence: [1, 3, 3, 3, 1, 1, 1, 2, 2, 2, 1, 3, 1, 2, 2, 1, 1, 3, 3, 1, 2, 2, 2, 1, 3, 3, 1, 1, 2, 1]

Possible Kolakoski sequence? true

Starting sequence: [1, 3, 2, 1]

Kolakoski sequence: [1, 3, 3, 3, 2, 2, 2, 1, 1, 1, 1, 1, 3, 3, 2, 2, 1, 1, 3, 2, 1, 1, 1, 1, 3, 3, 3, 2, 2, 1]

Possible Kolakoski sequence? false

</pre>