1 files changed, 37 insertions, 0 deletions
diff --git a/test/math/kthperm.cpp b/test/math/kthperm.cpp
new file mode 100644
index 0000000..8115356
--- /dev/null
+++ b/test/math/kthperm.cpp
@@ -0,0 +1,37 @@
+#include "../util.h"
+#include <math/kthperm.cpp>
+
+void stress_test() {
+	ll queries = 0;
+	for (ll i = 0; i < 10'000; i++) {
+		int n = Random::integer<int>(1, 100);
+		vector<ll> expected(n);
+		iota(all(expected), 0);
+		ll k = 0;
+		do {
+			auto got = kthperm(n, k);
+			if (got != expected) cerr << "error" << FAIL;
+			k++;
+		} while (k < 100 && next_permutation(all(expected)));
+		queries += n;
+	}
+	cerr << "tested queries: " << queries << endl;
+}
+
+constexpr int N = 500'000;
+void performance_test() {
+	timer t;
+	t.start();
+	auto got = kthperm(N, 4'168'751'907'498'170ll);
+	t.stop();
+	hash_t hash = 0;
+	for (ll i = 0; i < N; i++) hash += i * got[i];
+	if (t.time > 500) cerr << "too slow: " << t.time << FAIL;
+	cerr << "tested performance: " << t.time << "ms (hash: " << hash << ")" << endl;
+}
+
+int main() {
+	stress_test();
+	performance_test();
+}
+