a0e1cde063
The two-way block diff (yjs-body-merge.diffBlocks) and the three-way merge planner (three-way-merge.lcsPairs) built the identical backward-filled LCS DP table inline. Extract it to lcs.ts (buildLcsTable); each caller keeps its own traceback. No behavior change — merge specs unchanged and green. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
27 lines
913 B
TypeScript
27 lines
913 B
TypeScript
/**
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* Backward-filled LCS length table for sequences `a` and `b`: `dp[i][j]` is the
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* length of the longest common subsequence of the suffixes `a[i:]` and `b[j:]`.
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* O(n*m) time/space — fine for page block counts.
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*
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* Shared by the two-way block diff (`yjs-body-merge.diffBlocks`) and the
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* three-way merge planner (`three-way-merge.lcsPairs`) so the (identical) table
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* construction lives in ONE place; each caller does its own traceback over the
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* returned table.
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*/
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export function buildLcsTable(a: string[], b: string[]): number[][] {
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const n = a.length;
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const m = b.length;
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const dp: number[][] = Array.from({ length: n + 1 }, () =>
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new Array(m + 1).fill(0),
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);
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for (let i = n - 1; i >= 0; i--) {
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for (let j = m - 1; j >= 0; j--) {
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dp[i][j] =
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a[i] === b[j]
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? dp[i + 1][j + 1] + 1
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: Math.max(dp[i + 1][j], dp[i][j + 1]);
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}
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}
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return dp;
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}
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