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Commit d88104c

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Improve partial_sort_copy
1 parent e1a8b5e commit d88104c

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2 files changed

+51
-25
lines changed

2 files changed

+51
-25
lines changed

‎array_alg.h

Lines changed: 21 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -2127,31 +2127,36 @@ ALGDEF T *NS(partial_sort_copy)(
21272127
void *compare_ctx
21282128
)
21292129
{
2130-
size_t n1 = last - first;
2131-
size_t n2 = out_last - out_first;
2132-
2133-
size_t n = (n2 < n1) ? n2 : n1;
2134-
out_last = out_first + n;
2135-
2136-
if (n == 0) { return out_last; }
2137-
2138-
NS(copy_n)(first, n, out_first);
2139-
first += n;
2130+
if (first == last || out_first == out_last) return out_first;
2131+
T *out = out_first;
2132+
*out = *first;
2133+
++out;
2134+
++first;
21402135

2141-
NS(make_heap_n)(out_first, n, compare, compare_ctx);
2136+
while (out != out_last)
2137+
{
2138+
if (first == last) {
2139+
NS(sort_heap)(out_first, out, compare, compare_ctx);
2140+
return out;
2141+
}
2142+
*out = *first;
2143+
++first;
2144+
++out;
2145+
NS(push_heap)(out_first, out, compare, compare_ctx);
2146+
}
21422147

21432148
while (first != last)
21442149
{
21452150
if (compare(first, out_first, compare_ctx) < 0)
21462151
{
2147-
NS(pop_heap_n)(out_first, n, compare, compare_ctx);
2148-
*(out_last - 1) = *first;
2149-
NS(push_heap_n)(out_first, n, compare, compare_ctx);
2152+
NS(pop_heap)(out_first, out, compare, compare_ctx);
2153+
*(out - 1) = *first;
2154+
NS(push_heap)(out_first, out, compare, compare_ctx);
21502155
}
21512156
++first;
21522157
}
2153-
NS(sort_heap)(out_first, out_last, compare, compare_ctx);
2154-
return out_last;
2158+
NS(sort_heap)(out_first, out, compare, compare_ctx);
2159+
return out;
21552160
}
21562161

21572162
ALGDEF void NS(nth_element)(

‎test/tests.c

Lines changed: 30 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -590,19 +590,40 @@ void test_partial_sort() {
590590
}
591591

592592
void test_partial_sort_copy() {
593-
enum { N = 100 };
594-
int nums[N];
595-
for (int i = 0; i < N; ++i) {
596-
nums[i] = i;
593+
{
594+
enum { N = 100 };
595+
int nums[N];
596+
for (int i = 0; i < N; ++i) {
597+
nums[i] = i;
598+
}
599+
600+
enum { M = 10 };
601+
for (int iteration = 0; iteration < 1000; ++iteration) {
602+
intv_random_shuffle(nums, nums + N);
603+
604+
int top[M];
605+
intv_partial_sort_copy(nums, nums + N, top, top + M, compare_int, NULL);
606+
607+
for (int i = 0; i < M; ++i) {
608+
assert(top[i] == i);
609+
}
610+
}
597611
}
612+
{
613+
enum { N = 10 };
614+
int nums[N];
615+
for (int i = 0; i < N; ++i) {
616+
nums[i] = i;
617+
}
618+
intv_reverse(nums, nums + N);
598619

599-
for (int iteration = 0; iteration < 1000; ++iteration) {
600-
intv_random_shuffle(nums, nums + N);
620+
enum { M = 100 };
601621

602-
int top[10];
603-
intv_partial_sort_copy(nums, nums + N, top, top + 10, compare_int, NULL);
622+
int top[M];
623+
int *out = intv_partial_sort_copy(nums, nums + N, top, top + M, compare_int, NULL);
624+
assert(out == top + N);
604625

605-
for (int i = 0; i < 10; ++i) {
626+
for (int i = 0; i < N; ++i) {
606627
assert(top[i] == i);
607628
}
608629
}

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