day15

1 files changed, 29 insertions, 0 deletions

diff --git a/day15.cc b/day15.cc
new file mode 100644
index 0000000..55a3d6d
--- /dev/null
+++ b/day15.cc
@@ -0,0 +1,29 @@
+#include <iostream>
+
+using namespace std;
+
+template <int const n=0>
+struct lrng {
+	uint64_t m, s;
+	uint16_t operator*() const { return s; }
+	auto operator++() { do s = s * m % 2147483647; while (n && s % n != 0); }
+};
+
+int
+main() {
+	int p1{0}, p2{0};
+
+	lrng<> a1{16807, 634};
+	lrng<> b1{48271, 301};
+	for (long i{0}; i < 40'000'000; ++i, ++a1, ++b1)
+		if (*a1 == *b1)
+			p1++;
+
+	lrng<4> a2{16807, 634};
+	lrng<8> b2{48271, 301};
+	for (long i{0}; i < 5'000'000; ++i, ++a2, ++b2)
+		if (*a2 == *b2)
+			p2++;
+
+	cout << p1 << endl << p2 << endl;	// 573 294
+}