From 0f1223c5396961a661da4f12caf0252f924de01b Mon Sep 17 00:00:00 2001
From: Gloria Mundi <gloria@gloria-mundi.eu>
Date: Wed, 19 Feb 2025 21:29:03 +0100
Subject: reverse dynamic convex hull

---
 content/datastructures/dynamicConvexHull.cpp     | 6 +++---
 test/datastructures/dynamicConvexHull.cpp        | 4 ++--
 test/datastructures/dynamicConvexHull.lichao.cpp | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/content/datastructures/dynamicConvexHull.cpp b/content/datastructures/dynamicConvexHull.cpp
index 36ef6f5..3e4020e 100644
--- a/content/datastructures/dynamicConvexHull.cpp
+++ b/content/datastructures/dynamicConvexHull.cpp
@@ -1,16 +1,16 @@
 struct Line {
 	mutable ll m, c, p;
-	bool operator<(const Line& o) const { return m < o.m; }
+	bool operator<(const Line& o) const { return m > o.m; }
 	bool operator<(ll x) const { return p < x; }
 };
 
-struct HullDynamic : multiset<Line, less<>> { // max über Geraden
+struct HullDynamic : multiset<Line, less<>> { // min über Geraden
 	// (for doubles, use INF = 1/.0, div(a,c) = a/c)
 	ll div(ll a, ll c) { return a / c - ((a ^ c) < 0 && a % c); }
 
 	bool isect(iterator x, iterator y) {
 		if (y == end()) { x->p = INF; return false; }
-		if (x->m == y->m) x->p = x->c > y->c ? INF : -INF;
+		if (x->m == y->m) x->p = x->c < y->c ? INF : -INF;
 		else x->p = div(y->c - x->c, x->m - y->m);
 		return x->p >= y->p;
 	}
diff --git a/test/datastructures/dynamicConvexHull.cpp b/test/datastructures/dynamicConvexHull.cpp
index e0345af..02e50f4 100644
--- a/test/datastructures/dynamicConvexHull.cpp
+++ b/test/datastructures/dynamicConvexHull.cpp
@@ -29,7 +29,7 @@ void stress_test(ll range) {
 
 				ll got = hd.query(x);
 				ll expected = naive[0](x);
-				for (auto l : naive) expected = max(expected, l(x));
+				for (auto l : naive) expected = min(expected, l(x));
 
 				if (got != expected) cerr << "got: " << got << ", expected: " << expected << FAIL;
 				queries++;
@@ -49,7 +49,7 @@ void performance_test() {
 		ll m = Random::integer<ll>(-1'000'000'000, 1'000'000'000);
 		ll c = Random::integer<ll>(-1'000'000'000, 1'000'000'000);
 		ll x = Random::integer<ll>(-1'000'000'000, 1'000'000'000);
-		
+
 		t.start();
 		hd.add(m, c);
 		hash += hd.query(x);
diff --git a/test/datastructures/dynamicConvexHull.lichao.cpp b/test/datastructures/dynamicConvexHull.lichao.cpp
index 9a6ffb9..f692e92 100644
--- a/test/datastructures/dynamicConvexHull.lichao.cpp
+++ b/test/datastructures/dynamicConvexHull.lichao.cpp
@@ -16,11 +16,11 @@ void stress_test(ll range) {
 			ll m = Random::integer<ll>(-range, range);
 			ll c = Random::integer<ll>(-range, range);
 			hd.add(m, c);
-			lichao.insert({-m, -c});
+			lichao.insert({m, c});
 
 			for (ll x : xs) {
 				ll gotA = hd.query(x);
-				ll gotB = -lichao.query(x);
+				ll gotB = lichao.query(x);
 
 				if (gotA != gotB) cerr << "gotA: " << gotA << ", gotB: " << gotB << FAIL;
 				queries++;
-- 
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