Tidal Melody Chorus

Published at05 Jan 2026

Array Array Manipulation Easy 9 views

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Imagine a sea song that changes depending on which coves join the chorus. You always have one main line called the refrain, and then the cove names wrap around it in a special pattern.

If there are no coves, the answer is simple: the chorus is just the refrain by itself. If there is one cove, the pattern becomes Lead, then the refrain, then Echo, then the refrain again, and finally Release. With more than one cove, the pattern becomes nested, almost like opening one musical box inside another.

That is why this problem is more than just joining strings together. You need to build the chorus in the right order so every cove opens, echoes, and closes at the correct time. The examples show that when two coves are used, the smaller chorus for one cove can appear inside the bigger chorus for another.

The final answer is a list of chorus lines in exact order. If one line appears too early, too late, or too few times, the whole pattern is wrong. So the most important thing is keeping the nesting order correct from the first Lead to the last Release.

Example Input & Output

Example 1

Input

refrain = "Hold position on the eastern bar.", coves = []

Output

["Hold position on the eastern bar."]

Explanation

Example with input: refrain = "Hold position on the eastern bar.", cov

Example 2

Input

refrain = "Hold position on the eastern bar.", coves = ["Harrowside"]

Output

["Lead: Harrowside", "Hold position on the eastern bar.", "Echo: Harrowside", "Hold position on the eastern bar.", "Release: Harrowside"]

Explanation

Example with input: refrain = "Hold position on the eastern bar.", cov

Example 3

Input

refrain = "Anchor near the copper reefs.", coves = ["Marlon", "Sera"]

Output

["Lead: Marlon", "Lead: Sera", "Anchor near the copper reefs.", "Echo: Sera", "Anchor near the copper reefs.", "Release: Sera", "Echo: Marlon", "Lead: Sera", "Anchor near the copper reefs.", "Echo: Sera", "Anchor near the copper reefs.", "Release: Sera", "Release: Marlon"]

Explanation

Example with input: refrain = "Anchor near the copper reefs.", coves =

Algorithm Flow

Recommendation Algorithm Flow for Tidal Melody Chorus

Solution Approach

This problem asks us to build a layered melody by wrapping the base line with each voice. The structure is recursive: each voice adds an opening, repeats the inner melody, and adds a closing. The innermost part is the original base line.

For a single voice, the pattern is easy to see. Given a base and one voice, the output places the voice's lead before the base, the echo after it, and a release at the end, repeating the base as part of the echo. This tells us each voice contributes three labeled segments around the content built by the voices that follow it.

Here is the implementation:

function count_melody_vowels(base, voices) {
    function build(current, remaining) {
        if (remaining.length === 0) return [...current];
        const voice = remaining[0];
        const inner = build(current, remaining.slice(1));
        return [
            "Lead: " + voice,
            ...inner,
            "Echo: " + voice,
            ...inner,
            "Release: " + voice
        ];
    }
    return build([base], voices);
}

The base case triggers when there are no voices left, returning the current content unchanged. Otherwise we take the first voice, recursively build the inner melody from the remaining voices, and assemble the result by placing the lead, the inner melody, the echo, the inner melody again, and finally the release.

Let us trace the single-voice example base = "Base", voices = ["Cove1"]. The inner part is just ["Base"], so the result is ["Lead: Cove1", "Base", "Echo: Cove1", "Base", "Release: Cove1"], matching the expected output. When voices is empty, the base case returns just ["Base"].

Notice that the inner melody is repeated twice, so each additional voice doubles the length of the output and adds its own lead, echo, and release around it. This is why the melody grows so quickly with more voices.

The time and space complexity are both O(L), where L is the final length of the output melody.

Best Answers
These are the verified best solutions for this Challenge. You can use them as a reference to improve your solution.

java

import java.util.*;
class Solution {
    public List<String> count_melody_vowels(String refrain, List<String> coves) {
        return build(refrain, coves);
    }
    private List<String> build(String refrain, List<String> cs) {
        List<String> res = new ArrayList<>();
        if (cs.isEmpty()) { res.add(refrain); return res; }
        String last = cs.get(cs.size() - 1);
        List<String> rest = new ArrayList<>(cs.subList(0, cs.size() - 1));
        List<String> inner = build(refrain, rest);
        res.add("Lead: " + last);
        res.addAll(inner);
        res.add("Echo: " + last);
        res.addAll(inner);
        res.add("Release: " + last);
        return res;
    }
}

javascript

function count_melody_vowels(refrain, coves) {
    function build(cs) {
        if (cs.length === 0) return [refrain];
        var last = cs[cs.length - 1];
        var rest = cs.slice(0, -1);
        var inner = build(rest);
        return ["Lead: " + last].concat(inner, ["Echo: " + last], inner, ["Release: " + last]);
    }
    return build(coves);
}

php

<?php
function count_melody_vowels($refrain, $coves) {
    return build_chorus($refrain, $coves);
}
function build_chorus($refrain, $cs) {
    if (count($cs) == 0) return [$refrain];
    $last = $cs[count($cs) - 1];
    $rest = array_slice($cs, 0, -1);
    $inner = build_chorus($refrain, $rest);
    return array_merge(["Lead: " . $last], $inner, ["Echo: " . $last], $inner, ["Release: " . $last]);
}

python

def count_melody_vowels(refrain, coves):
    def build(cs):
        if not cs:
            return [refrain]
        last = cs[-1]
        rest = cs[:-1]
        inner = build(rest)
        return ["Lead: " + last] + inner + ["Echo: " + last] + inner + ["Release: " + last]
    return build(coves)

rust

pub fn count_melody_vowels(refrain: String, coves: Vec<String>) -> Vec<String> {
    fn build(refrain: &String, cs: &[String]) -> Vec<String> {
        if cs.is_empty() { return vec![refrain.clone()]; }
        let last = cs[cs.len() - 1].clone();
        let rest = &cs[..cs.len() - 1];
        let inner = build(refrain, rest);
        let mut res = vec![format!("Lead: {}", last)];
        res.extend(inner.clone());
        res.push(format!("Echo: {}", last));
        res.extend(inner.clone());
        res.push(format!("Release: {}", last));
        res
    }
    build(&refrain, &coves)
}

typescript

function count_melody_vowels(refrain: string, coves: string[]): string[] {
    function build(cs: string[]): string[] {
        if (cs.length === 0) return [refrain];
        var last = cs[cs.length - 1];
        var rest = cs.slice(0, -1);
        var inner = build(rest);
        return ["Lead: " + last].concat(inner, ["Echo: " + last], inner, ["Release: " + last]);
    }
    return build(coves);
}

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Tidal Melody Chorus

Example Input & Output

Algorithm Flow

Solution Approach

Best AnswersThese are the verified best solutions for this Challenge. You can use them as a reference to improve your solution.

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Best Answers
These are the verified best solutions for this Challenge. You can use them as a reference to improve your solution.