add min mod (mimumum of linear function modulo m)

1 files changed, 92 insertions, 0 deletions

diff --git a/test/math/minMod.cpp b/test/math/minMod.cpp
new file mode 100644
index 0000000..e49da11
--- /dev/null
+++ b/test/math/minMod.cpp
@@ -0,0 +1,92 @@
+#include "../util.h"
+#include <math/shortModInv.cpp>
+#include <math/minMod.cpp>
+
+ll naiveMinMod(ll n, ll m, ll a, ll b){
+	ll ans = m;
+	for(ll i = 0; i < n; i++){
+		ans = min(ans, (a*i+b)%m);
+	}
+	return ans;
+}
+
+ll naiveFirstVal(ll a, ll m, ll l, ll r){
+	for(ll i = 0; i < m; i++){
+		ll v = a*i % m;
+		if(l <= v && v <= r) return v;
+	}
+	return -1;
+}
+
+void stress_test_minMod() {
+	ll queries = 0;
+	for (ll i = 0; i < 10'000; i++) {
+		int n = Random::integer<int>(1, 100);
+		int m = Random::integer<int>(1, 100);
+		int a = Random::integer<int>(0, m);
+		int b = Random::integer<int>(0, m);
+		ll expected = naiveMinMod(n, m, a, b);
+		ll got = minMod(n, m, a, b);
+		if (got != expected) cerr << "got: " << got << ", expected: " << expected << FAIL;
+		queries++;
+	}
+	cerr << "tested queries: " << queries << endl;
+}
+
+void stress_test_firstVal() {
+	ll queries = 0;
+	for (ll i = 0; i < 10'000; i++) {
+		int m = Random::integer<int>(1, 100);
+		int a = Random::integer<int>(0, m);
+		int l = Random::integer<int>(0, m);
+		int r = Random::integer<int>(0, m);
+		if(l > r) swap(l, r);
+		ll expected = naiveFirstVal(a, m, l, r);
+		ll got = firstVal(a, m, l, r);
+		if (got != expected) cerr << a << " " << m << " " << l << " " << r << "got: " << got << ", expected: " << expected << FAIL;
+		queries++;
+	}
+	cerr << "tested queries: " << queries << endl;
+}
+
+constexpr int N = 1'000'000;
+void performance_test_minMod() {
+	timer t;
+	hash_t hash = 0;
+	for (int operations = 0; operations < N; operations++) {
+		ll n = Random::integer<ll>(1, 1'000'000'000);
+		ll m = Random::integer<ll>(1, 1'000'000'000);
+		ll a = Random::integer<ll>(0, m);
+		ll b = Random::integer<ll>(0, m);
+		t.start();
+		hash += minMod(n, m, a, b);
+		t.stop();
+	}
+	if (t.time > 750) cerr << "too slow: " << t.time << FAIL;
+	cerr << "tested performance: " << t.time << "ms (hash: " << hash << ")" << endl;
+}
+
+void performance_test_firstVal() {
+	timer t;
+	hash_t hash = 0;
+	for (int operations = 0; operations < N; operations++) {
+		ll m = Random::integer<ll>(1, 1'000'000'000);
+		ll a = Random::integer<ll>(1, m);
+		ll l = Random::integer<ll>(0, m);
+		ll r = Random::integer<ll>(0, m);
+		if(l > r) swap(l, r);
+		t.start();
+		hash += firstVal(a, m, l, r);
+		t.stop();
+	}
+	if (t.time > 750) cerr << "too slow: " << t.time << FAIL;
+	cerr << "tested performance: " << t.time << "ms (hash: " << hash << ")" << endl;
+}
+
+int main() {
+	stress_test_minMod();
+	stress_test_firstVal();
+	performance_test_minMod();
+	performance_test_firstVal();
+}
+