1 files changed, 43 insertions, 0 deletions
diff --git a/test/math/inversions.cpp b/test/math/inversions.cpp
new file mode 100644
index 0000000..d2a54b7
--- /dev/null
+++ b/test/math/inversions.cpp
@@ -0,0 +1,43 @@
+#include "../util.h"
+#include <datastructures/pbds.cpp>
+#include <math/inversions.cpp>
+
+ll naive(const vector<ll>& v) {
+	ll res = 0;
+	for (ll i = 0; i < sz(v); i++) {
+		for (ll j = 0; j < i; j++) {
+			if (v[j] > v[i]) res++;
+		}
+	}
+	return res;
+}
+
+void stress_test() {
+	ll queries = 0;
+	for (ll i = 0; i < 100'000; i++) {
+		int n = Random::integer<int>(1, 100);
+		auto v = Random::integers<ll>(n, -50, 50);
+		ll got = inversions(v);
+		ll expected = naive(v);
+		if (got != expected) cerr << "got: " << got << ", expected: " << expected << FAIL;
+		queries += n;
+	}
+	cerr << "tested queries: " << queries << endl;
+}
+
+constexpr int N = 200'000;
+void performance_test() {
+	timer t;
+	auto v = Random::integers<ll>(N, -10'000, 10'000);
+	t.start();
+	hash_t hash = inversions(v);
+	t.stop();
+	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();
+}
+