3163-string-compression-iii.rb

# frozen_string_literal: true

# 3163. String Compression III
# Medium
# https://leetcode.com/problems/string-compression-iii/description/

=begin
Given a string word, compress it using the following algorithm:
* Begin with an empty string comp. While word is not empty, use the following operation:
  * Remove a maximum length prefix of word made of a single character c repeating at most 9 times.
  * Append the length of the prefix followed by c to comp.
Return the string comp.

Example 1:
Input: word = "abcde"
Output: "1a1b1c1d1e"
Explanation:
Initially, comp = "". Apply the operation 5 times, choosing "a", "b", "c", "d", and "e" as the prefix in each operation.
For each prefix, append "1" followed by the character to comp.

Example 2:
Input: word = "aaaaaaaaaaaaaabb"
Output: "9a5a2b"
Explanation:
Initially, comp = "". Apply the operation 3 times, choosing "aaaaaaaaa", "aaaaa", and "bb" as the prefix in each operation.
* For prefix "aaaaaaaaa", append "9" followed by "a" to comp.
* For prefix "aaaaa", append "5" followed by "a" to comp.
* For prefix "bb", append "2" followed by "b" to comp.

Constraints:
* 1 <= word.length <= 2 * 105
* word consists only of lowercase English letters.
=end

# @param {String} word
# @return {String}
def compressed_string(word)
  word.gsub(/(.)\1{,8}/) { _1.size.to_s + $1 }
end

# **************** #
#       TEST       #
# **************** #

require "test/unit"
class Test_compressed_string < Test::Unit::TestCase
  def test_
    assert_equal "1a1b1c1d1e", compressed_string("abcde")
    assert_equal "9a5a2b", compressed_string("aaaaaaaaaaaaaabb")
  end
end