• Can we assume the strings are ASCII?
  • Yes
• Is case important?
  • The strings are lower case
• Can we assume the inputs are valid?
  • No, check for None
• Can we assume this fits memory?
  • Yes

Instructions:

• Program should be written in file build.py

• Function name should be find_diff.

• Input

   Type:  String
   Value: s1 = 'aabcddd'
   	      s2 = 'abbbbccde'
  

• Expected Output

    Type:  String
    Value: 'e'