string incrementer

Your job is to write a function which increments a string, to create a new string. If the string already ends with a number, the number should be incremented by 1. If the string does not end with a number the number 1 should be appended to the new string.

Examples:

foo -> foo1

foobar23 -> foobar24

foo0042 -> foo0043

foo9 -> foo10

foo099 -> foo100

Answer

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def (input)
  
  return "1" if input.empty?
  arr = input.rpartition(/D/)
  if arr[-1].empty?
   arr[-1] = "1"
  else
    arr[-1] = arr[-1].succ
  end
  return arr.join
end

def (input)
  input.sub(/d*$/) { |n| n.empty? ? 1 : n.succ }
end