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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>
maint
Meet Soni 2025-02-14 10:11:29 +05:30 committed by Junio C Hamano
parent e2067b49ec
commit b07dd9078b
1 changed files with 7 additions and 8 deletions
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15
merge-recursive.c
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@ -2758,23 +2758,22 @@ static int process_renames(struct merge_options *opt,
const struct rename *sre;

/*
* FIXME: As string-list.h notes, it's O(n^2) to build a sorted
* string_list one-by-one, but O(n log n) to build it unsorted and
* then sort it. Note that as we build the list, we do not need to
* check if the existing destination path is already in the list,
* because the structure of diffcore_rename guarantees we won't
* have duplicates.
* Note that as we build the list, we do not need to check if the
* existing destination path is already in the list, because the
* structure of diffcore_rename guarantees we won't have duplicates.
*/
for (i = 0; i < a_renames->nr; i++) {
sre = a_renames->items[i].util;
string_list_insert(&a_by_dst, sre->pair->two->path)->util
string_list_append(&a_by_dst, sre->pair->two->path)->util
= (void *)sre;
}
for (i = 0; i < b_renames->nr; i++) {
sre = b_renames->items[i].util;
string_list_insert(&b_by_dst, sre->pair->two->path)->util
string_list_append(&b_by_dst, sre->pair->two->path)->util
= (void *)sre;
}
string_list_sort(&a_by_dst);
string_list_sort(&b_by_dst);

for (i = 0, j = 0; i < a_renames->nr || j < b_renames->nr;) {
struct string_list *renames1, *renames2Dst;