merge-recursive: optimize time complexity for process_renames
Avoid O(n^2) complexity in `process_renames()` when building a sorted `string_list` by constructing it unsorted and sorting it afterward, reducing the complexity to O(n log n). Signed-off-by: Meet Soni <meetsoni3017@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Meet Soni committed
Feb 14, 2025 at 10:11 UTC
b07dd9078b8ba5f3b7f5c88f84f7ee9c34fa65e1
1 file changed
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-8
merge-recursive.c
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@@ -2758,23 +2758,22 @@ static int process_renames(struct merge_options *opt,
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const struct rename *sre;
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/*
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- * FIXME: As string-list.h notes, it's O(n^2) to build a sorted
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- * string_list one-by-one, but O(n log n) to build it unsorted and
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- * then sort it. Note that as we build the list, we do not need to
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- * check if the existing destination path is already in the list,
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- * because the structure of diffcore_rename guarantees we won't
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- * have duplicates.
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+ * Note that as we build the list, we do not need to check if the
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+ * existing destination path is already in the list, because the
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+ * structure of diffcore_rename guarantees we won't have duplicates.
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*/
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for (i = 0; i < a_renames->nr; i++) {
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sre = a_renames->items[i].util;
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- string_list_insert(&a_by_dst, sre->pair->two->path)->util
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+ string_list_append(&a_by_dst, sre->pair->two->path)->util
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= (void *)sre;
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}
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for (i = 0; i < b_renames->nr; i++) {
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sre = b_renames->items[i].util;
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- string_list_insert(&b_by_dst, sre->pair->two->path)->util
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+ string_list_append(&b_by_dst, sre->pair->two->path)->util
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= (void *)sre;
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}
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+ string_list_sort(&a_by_dst);
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+ string_list_sort(&b_by_dst);
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for (i = 0, j = 0; i < a_renames->nr || j < b_renames->nr;) {
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struct string_list *renames1, *renames2Dst;