count_and_say.rb

# https://leetcode.com/problems/count-and-say/
#
# The count-and-say sequence is the sequence of integers beginning as follows:
#
#     1, 11, 21, 1211, 111221, ...
#
#      1 is read off as "one 1" or 11.
#     11 is read off as "two 1s" or 21.
#     21 is read off as "one 2, then one 1" or 1211.
#
# Given an integer n, generate the nth sequence.
#
# Note: The sequence of integers will be represented as a string.


# @param {Integer} n
# @return {String}
def count_and_say(n)
  str = '1'

  n -= 1
  n.times do
    char, count, newstr = str[0], 1, ''

    str[1..-1].each_char do |ch|
      if ch == char
        count += 1
      else
        newstr << count.to_s << char
        char, count = ch, 1
      end
    end
    newstr << count.to_s << char

    str = newstr
  end

  str
end