Find first available serial based on list of strings?

Question

Given a list of strings such as: apple01, apple02, and apple04, banana02, cherry01, how would you come up with t

Answer 1

if the name that occurs first is pure letters not including any number and than followed by a number . that would be easy and you can get the index of the first number or char that exists in that char list {1,2,3,4,5,6,7,8,9} and than you can make substring(0,indexof(firstnumber))