new linear recurrence kthTerm code

1 files changed, 67 insertions, 0 deletions

diff --git a/test/math/linearRecurrenceSlowMul.cpp b/test/math/linearRecurrenceSlowMul.cpp
new file mode 100644
index 0000000..205e584
--- /dev/null
+++ b/test/math/linearRecurrenceSlowMul.cpp
@@ -0,0 +1,67 @@
+#include "../util.h"
+
+constexpr ll mod = 998244353;
+vector<ll> mul(const vector<ll> &a, const vector<ll> &b){
+	vector<ll> c(sz(a) + sz(b) - 1);
+	for(int i = 0; i < sz(a); i++){
+		for(int j = 0; j < sz(b); j++){
+			c[i+j] += a[i]*b[j] % mod;
+		}
+	}
+	for(ll &x : c) x %= mod;
+	return c;
+}
+
+#include <math/linearRecurrence.cpp>
+
+struct RandomRecurence {
+	vector<ll> f, c, cache;
+	RandomRecurence(int n) : f(Random::integers<ll>(n, 0, mod)), c(Random::integers<ll>(n, 0, mod)), cache(f) {}
+
+	ll operator()(ll k){
+		while (sz(cache) <= k) {
+			ll cur = 0;
+			for (ll i = 0; i < sz(c); i++) {
+				cur += (c[i] * cache[sz(cache) - i - 1]) % mod;
+			}
+			cur %= mod;
+			cache.push_back(cur);
+		}
+		return cache[k];
+	}
+};
+
+void stress_test() {
+	int queries = 0;
+	for (int i = 0; i < 10'000; i++) {
+		int n = Random::integer<int>(1, 10);
+		RandomRecurence f(n);
+		for (int j = 0; j < 100; j++) {
+			ll k = Random::integer<ll>(0, 1000);
+
+			ll got = kthTerm(f.f, f.c, k);
+			ll expected = f(k);
+
+			if (got != expected) cerr << "got: " << got << ", expected: " << expected << FAIL;
+			queries++;
+		}
+	}
+	cerr << "tested random queries: " << queries << endl;
+}
+
+constexpr int N = 1'000;
+void performance_test() {
+	timer t;
+	RandomRecurence f(N);
+	t.start();
+	hash_t hash = kthTerm(f.f, f.c, 1e18);
+	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();
+}
+