1 files changed, 73 insertions, 0 deletions

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);
+}