From 756f22d58bb198b8f34589c112e1003614ccdcd6 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 2 Nov 2025 21:41:58 +0100
Subject: aoc 2017, days 1-20

---
 2017/src/day15.cpp | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 2017/src/day15.cpp

(limited to '2017/src/day15.cpp')

diff --git a/2017/src/day15.cpp b/2017/src/day15.cpp
new file mode 100644
index 0000000..270528b
--- /dev/null
+++ b/2017/src/day15.cpp
@@ -0,0 +1,73 @@
+#include <iostream>
+
+using namespace std;
+
+namespace {
+
+struct Generator {
+	Generator(unsigned long factor, unsigned long prev)
+	    : factor{ factor }
+	    , prev{ prev }
+	{
+	}
+
+	unsigned long next()
+	{
+		prev *= factor;
+		prev %= 2147483647;
+		return prev;
+	}
+
+	unsigned long factor;
+	unsigned long prev;
+};
+
+void
+part1(unsigned long start_a, unsigned long start_b)
+{
+	Generator GenA(16807, start_a);
+	Generator GenB(48271, start_b);
+
+	int count = 0;
+	for ( int i = 0; i != 40000000; ++i ) {
+		if ( (GenA.next() & 0xFFFF) == (GenB.next() & 0xFFFF) ) {
+			++count;
+		}
+	}
+	cout << "Part1: " << count << '\n';
+}
+
+void
+part2(unsigned long start_a, unsigned long start_b)
+{
+	Generator GenA(16807, start_a);
+	Generator GenB(48271, start_b);
+
+	int count = 0;
+	for ( int i = 0; i != 5000000; ++i ) {
+		auto value_a = GenA.next();
+		while ( value_a % 4 != 0 ) {
+			value_a = GenA.next();
+		}
+		auto value_b = GenB.next();
+		while ( value_b % 8 != 0 ) {
+			value_b = GenB.next();
+		}
+		if ( (value_a & 0xFFFF) == (value_b & 0xFFFF) ) {
+			++count;
+		}
+	}
+	cout << "Part2: " << count << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+	static const unsigned long start_a = 618;
+	static const unsigned long start_b = 814;
+
+	part1(start_a, start_b);
+	part2(start_a, start_b);
+}
-- 
cgit v1.3