How to Track and Diff Text Changes: Git Diff, Myers Algorithm, and LCS Explained
Ever wondered how Git produces clean pull request diffs? Explore graph search, edit distance, and Longest Common Subsequence algorithms behind text comparison.
Introduction: The Core of Version Control
Every software developer relies on diff tools when reviewing GitHub pull requests or staging Git commits. But finding the minimal set of line additions and removals between two text files is a classic computer science challenge known as the Shortest Edit Script (SES) problem.
Longest Common Subsequence (LCS)
A common approach to diffing is finding the Longest Common Subsequence (LCS) between two sequences of lines:
- Construct a dynamic programming grid measuring common lines.
- Backtrack from the bottom-right corner to the origin.
- Lines present in both are labeled Unchanged; lines present only in the original are Removed (-); lines present only in the new version are Added (+).
Compare code files side-by-side with unified patch generation on our **Text Difference Tool**.
Frequently Asked Questions
Published by AnantAstra's engineering and research desk. All calculations, privacy guarantees, and algorithms referenced in this article are open-source and run client-side in the browser.
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