Solve: Double Up

Created By: Chris Taylor

/ Version: 2023.6.0

Write a method, doubleUp, that accepts a List<String> and returns a List<String> where each String in the original list is concatenated with itself. Your solution must not use loops and must use at least one lambda expression.

• ["a", "b"] -> ["aa", "bb"]
• ["", "last"] -> ["", "lastlast"]