2017 day16

1 files changed, 56 insertions, 1 deletions

diff --git a/src/2017/day15/aoc.cpp b/src/2017/day15/aoc.cpp
index bf7b729..756ccdd 100644
--- a/src/2017/day15/aoc.cpp
+++ b/src/2017/day15/aoc.cpp
@@ -2,5 +2,60 @@
 
 namespace aoc2017 {
 
-std::pair<int64_t, int64_t> day15(line_view) { return {0, 0}; }
+uint64_t generator(uint64_t x, uint64_t factor) { return x * factor % 2147483647; }
+
+bool lower16(uint64_t x) {
+  uint8_t i[8] = {0};
+  memcpy(i, &x, 8);
+  return i[0] == 0 && i[1] == 0;
+}
+
+int forty_million(uint64_t a, uint64_t b) {
+  int t{0};
+  constexpr size_t mi = 40 * 1000000;
+  for (size_t i = 0; i < mi; i++) {
+    a = generator(a, 16807);
+    b = generator(b, 48271);
+    t += (int)lower16(a ^ b);
+  }
+  return t;
+}
+
+int five_million(uint64_t a, uint64_t b) {
+  int t{0};
+  constexpr size_t mi = 5 * 1000000;
+  size_t p{0};
+  uint64_t n2[2] = {0, 0};
+  while (p < mi) {
+    if (n2[0] == 0) {
+      a = generator(a, 16807);
+      if (a % 4 == 0) {
+        n2[0] = a;
+      }
+    }
+    if (n2[1] == 0) {
+      b = generator(b, 48271);
+      if (b % 8 == 0) {
+        n2[1] = b;
+      }
+    }
+    if (n2[0] > 0 && n2[1] > 0) {
+      t += (int)lower16(n2[0] ^ n2[1]);
+      n2[0] = 0;
+      n2[1] = 0;
+      p++;
+    }
+  }
+  return t;
+}
+
+// Generator A starts with 873
+// Generator B starts with 583
+std::pair<int64_t, int64_t> day15(line_view) {
+  // uint64_t a = 65;
+  // uint64_t b = 8921;
+  uint64_t a = 873;
+  uint64_t b = 583;
+  return {forty_million(a, b), five_million(a, b)};
+}
 } // namespace aoc2017