Add LIS-based differentiator for minimal child reordering mutations (#56094)#56094
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javache wants to merge 1 commit intofacebook:mainfrom
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Add LIS-based differentiator for minimal child reordering mutations (#56094)#56094javache wants to merge 1 commit intofacebook:mainfrom
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…acebook#56094) Summary: The current Differentiator Stage 4 uses a greedy two-pointer algorithm to reconcile reordered children. When children are shuffled, it produces excessive REMOVE+INSERT pairs because it doesn't find the minimal edit. This adds an alternative code path that uses Longest Increasing Subsequence (LIS) to identify which children can stay in place vs which need to be moved. Items in the LIS maintain their relative order — only items outside the LIS need REMOVE+INSERT. Example: moving last element to front [A,B,C,D,E] → [E,A,B,C,D]: - Greedy: 4 REMOVEs + 5 INSERTs = 9 mutations - LIS: LIS=[A,B,C,D], only E moves = 1 REMOVE + 1 INSERT = 2 mutations The LIS algorithm is O(n log n) time, O(n) space. Since average child count is <10, the position mapping uses linear scan instead of hash tables. Guarded by `useLISAlgorithmInDifferentiator` feature flag (default off). Changelog: [Internal] Reviewed By: sammy-SC Differential Revision: D96334873
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…acebook#56094) Summary: Pull Request resolved: facebook#56094 The current Differentiator Stage 4 uses a greedy two-pointer algorithm to reconcile reordered children. When children are shuffled, it produces excessive REMOVE+INSERT pairs because it doesn't find the minimal edit. This adds an alternative code path that uses Longest Increasing Subsequence (LIS) to identify which children can stay in place vs which need to be moved. Items in the LIS maintain their relative order — only items outside the LIS need REMOVE+INSERT. Example: moving last element to front [A,B,C,D,E] → [E,A,B,C,D]: - Greedy: 4 REMOVEs + 5 INSERTs = 9 mutations - LIS: LIS=[A,B,C,D], only E moves = 1 REMOVE + 1 INSERT = 2 mutations The LIS algorithm is O(n log n) time, O(n) space. Since average child count is <10, the position mapping uses linear scan instead of hash tables. Guarded by `useLISAlgorithmInDifferentiator` feature flag (default off). Changelog: [Internal] Reviewed By: sammy-SC Differential Revision: D96334873
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Summary:
The current Differentiator Stage 4 uses a greedy two-pointer algorithm to
reconcile reordered children. When children are shuffled, it produces excessive
REMOVE+INSERT pairs because it doesn't find the minimal edit.
This adds an alternative code path that uses Longest Increasing Subsequence
(LIS) to identify which children can stay in place vs which need to be moved.
Items in the LIS maintain their relative order — only items outside the LIS
need REMOVE+INSERT.
Example: moving last element to front [A,B,C,D,E] → [E,A,B,C,D]:
The LIS algorithm is O(n log n) time, O(n) space. Since average child count
is <10, the position mapping uses linear scan instead of hash tables.
Guarded by
useLISAlgorithmInDifferentiatorfeature flag (default off).Changelog: [Internal]
Reviewed By: sammy-SC
Differential Revision: D96334873