Rosetta Code

Look-and-say sequence

Generate terms of the look-and-say sequence where each term describes the digits of the previous one.

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Sourcerosettacode/popular/look_and_say_sequence.vibe
type RunResult = { term_1: string, term_2: string, term_3: string, term_4: string, term_5: string }

def look_and_say(term: string) -> string
  term_chars = term.chars
  result = ""
  i = 0

  while i < term.length
    char = term_chars.fetch(i)
    count = 1
    while i + count < term.length && term_chars.fetch(i + count) == char
      count = count + 1
    end
    result = "#{result}#{count}#{char}"
    i = i + count
  end

  result
end

def sequence(n: int) -> array<string>
  terms = ["1"]
  i = 1
  while i < n
    terms.push(look_and_say(terms.fetch(i - 1)))
    i = i + 1
  end
  terms
end

def run -> RunResult
  {
    term_1: look_and_say("1"),
    term_2: look_and_say("11"),
    term_3: look_and_say("21"),
    term_4: look_and_say("1211"),
    term_5: look_and_say("111221")
  }
end

Output

Click Run example to see the result.

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