Problem

Given a text file and a variation of the file, identify lines that have been deleted, inserted, or changed.

I use this all the time in the form of the UNIX diff command.

• source code control: efficiently store multiple versions of a large program by keeping changes as ``diffs.''
• collaborative authoring: focus attention on new edits.
• software distribution: send updates as ``diffs'' instead of resending entire tree.
• debugging: compare the output of a newly compiled program to the correct output (can be used for grading also).