Diff Algorithms: Myers, Patience, and Histogram
Understand the algorithms behind diff tools: Myers shortest edit script, Patience diff for readable output, and Histogram diff used in Git.
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Tags: developer-tools, diff, algorithms
Diff Algorithms Explained: Myers, Patience, and Histogram Diffs Every time you run or open a pull request, a diff algorithm is deciding which lines to pair between the old and new version of a file. The algorithm choice affects whether the output is readable or confusing — whether moved functions look like total rewrites or clean relocations. Three algorithms dominate modern tooling: Myers (1986), Patience, and Histogram. Here's how each works and when to reach for each one. --- The Core Problem: Shortest Edit Script At its heart, file comparison is the Longest Common Subsequence (LCS) problem: find the largest set of lines that appear in both files in the same order. Everything not in that set is either added or deleted. The diff output is the shortest edit script — the minimum number of…
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