Common

Given an array A of strings made only from lowercase letters, 
return a list of all characters that show up in all strings within the list (including duplicates).  
For example, if a character occurs 3 times in all strings but not 4 times, 
you need to include that character three times in the final answer.

You may return the answer in any order.
 
Example 1:

Input: ["bella","label","roller"]
Output: ["e","l","l"]
Example 2:

Input: ["cool","lock","cook"]
Output: ["c","o"]

func commonChars(_ A: [String]) -> [String] {
        
}