Diff Checker
Compare two blocks of text side by side. See additions, deletions, and unchanged lines highlighted with a line-by-line LCS diff algorithm.
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How it worksText Diff Comparison (LCS Algorithm)
01Input
Two text inputs — original and modified — split into arrays of lines for comparison
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02LCS matrix
Longest Common Subsequence algorithm builds a matrix to find the optimal alignment between the two line arrays
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03Backtrack
Walk the LCS matrix backwards to classify each line as added (+), removed (−), or unchanged
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04Unified diff
Lines displayed with color coding — green for additions, red for deletions, gray for unchanged context
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05Stats
Summary shows total lines added, removed, and unchanged — helps quantify the scope of changes
Spec: Hunt–McIlroy diff algorithm, Unified diff format (GNU diffutils)
Line-by-line diff is the standard for code review. For character-level changes within a line, tools use a second pass of the same algorithm on individual characters.