comparing two collections for comparing two text files for additions, deletions, modifications

Question

I have two collections as below which hold IDs for Students.

The ids are Strings in the format 111-1111. e.g. of ids 221-2534, 215-6365, etc.

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Answer 1

If your files are not too large, maybe you can do the following steps

• Create a HashMap
• For every entry in old file, add it with value 'Old'
• For every entry in new file,
  • Check if it is in the HashMap
    • If so, then set value 'Both' (Additionally, you could add it to a HashMap of common elements)
    • If not, add it with value 'New'

This should hopefully address question 2. Please do let me know if it works. Thanks!