Subject: [PATCH] sparse-checkout: optimize string_list construction

From: amisha <[email-masked]>
Date: Fri, 16 Jan 2026 22:20:03 +0530

From: Amisha Chhajed <[email-masked]>

Improve O(n^2) complexity to O(n log n) while building a sorted
'string_list' by constructing it unsorted then sorting it
followed by removing duplicates.

Signed-off-by: Amisha Chhajed <[email-masked]>
---
 builtin/sparse-checkout.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index 15d51e60a8..7dfb276bf0 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -91,10 +91,11 @@ static int sparse_checkout_list(int argc, const char **argv, const char *prefix,
 
 		hashmap_for_each_entry(&pl.recursive_hashmap, &iter, pe, ent) {
 			/* pe->pattern starts with "/", skip it */
-			string_list_insert(&sl, pe->pattern + 1);
+			string_list_append(&sl, pe->pattern + 1);
 		}
 
 		string_list_sort(&sl);
+		string_list_remove_duplicates(&sl, 0);
 
 		for (i = 0; i < sl.nr; i++) {
 			quote_c_style(sl.items[i].string, NULL, stdout, 0);
@@ -289,7 +290,7 @@ static void write_cone_to_file(FILE *fp, struct pattern_list *pl)
 		if (!hashmap_contains_parent(&pl->recursive_hashmap,
 					     pe->pattern,
 					     &parent_pattern))
-			string_list_insert(&sl, pe->pattern);
+			string_list_append(&sl, pe->pattern);
 	}
 
 	string_list_sort(&sl);
@@ -311,7 +312,7 @@ static void write_cone_to_file(FILE *fp, struct pattern_list *pl)
 		if (!hashmap_contains_parent(&pl->recursive_hashmap,
 					     pe->pattern,
 					     &parent_pattern))
-			string_list_insert(&sl, pe->pattern);
+			string_list_append(&sl, pe->pattern);
 	}
 
 	strbuf_release(&parent_pattern);
-- 
2.51.0