LeetCode： Thousand Separator

Question

Given an integer n, add a dot (“.”) as the thousands separator and return it in string format.

Example 1:

Input: n = 987

Output: "987"

Example 2:

Input: n = 1234

Output: "1.234"

Example 3:

Input: n = 123456789

Output: "123.456.789"

Solution

def thousand_separator(n)
  i = 3
  length = n.to_s.length
  length = length + length / 4
  return n.to_s if length < 4

  while i < length
    n = n.to_s.reverse.insert(i, '.').reverse
    i += 4
  end
  n
end