Port day 22 to C++ for checking

Author: fwcd

day22/experiments/Makefile

@@ -0,0 +1,8 @@
+.PHONY: all
+all: out/day22
+
+out:
+	mkdir -p $@
+
+out/day22: ./day22.cpp | out
+	$(CXX) $< -Ofast -std=c++11 -o $@

day22/experiments/day22.cpp

@@ -0,0 +1,99 @@
+#include <cstdlib>
+#include <iostream>
+#include <fstream>
+#include <vector>
+
+const int LIMIT = 2000;
+
+int next(int secret) {
+  int mask = 16777215; // = 2^24 - 1
+  secret ^= secret << 6;
+  secret &= mask;
+  secret ^= secret >> 5;
+  secret &= mask;
+  secret ^= secret << 11;
+  secret &= mask;
+  return secret;
+}
+
+int prng(int secret, int n) {
+  for (int i = 0; i < n; i++) {
+    secret = next(secret);
+  }
+  return secret;
+}
+
+int monkey(int secret, int x1, int x2, int x3, int x4) {
+  int d1 = -1, d2 = -1, d3 = -1, d4 = -1;
+  for (int i = 0; i < LIMIT; i++) {
+    int lastPrice = secret % 10;
+    secret = next(secret);
+    int price = secret % 10;
+    d1 = d2;
+    d2 = d3;
+    d3 = d4;
+    d4 = price - lastPrice;
+    if (d1 == x1 && d2 == x2 && d3 == x3 && d4 == x4) {
+      return price;
+    }
+  }
+  return -1;
+}
+
+int score(std::vector<int> input, int x1, int x2, int x3, int x4) {
+  int sum = 0;
+  for (int n : input) {
+    int price = monkey(n, x1, x2, x3, x4);
+    if (price > 0) {
+      sum += price;
+    }
+  }
+  return sum;
+}
+
+int findBestScore(std::vector<int> input) {
+  int bestScore = 0;
+  int bound = 9;
+  for (int x1 = -bound; x1 <= bound; x1++) {
+    for (int x2 = -bound; x2 <= bound; x2++) {
+      std::cout << "Searching (" << x1 << ", " << x2 << ")" << std::endl;
+      for (int x3 = -bound; x3 <= bound; x3++) {
+        for (int x4 = -bound; x4 <= bound; x4++) {
+          int n = score(input, x1, x2, x3, x4);
+          if (n > bestScore) {
+            bestScore = n;
+          }
+        }
+      }
+    }
+  }
+  return bestScore;
+}
+
+int main(int argc, char *argv[]) {
+  if (argc == 1) {
+    std::cerr << "Usage: " << argv[0] << " <path to input>" << std::endl;
+    return 1;
+  }
+
+  std::vector<int> input;
+
+  {
+    std::ifstream file;
+    file.open(argv[1]);
+    for (std::string line; std::getline(file, line);) {
+      input.push_back(std::atoi(line.c_str()));
+    }
+  }
+
+  int part1 = 0;
+  for (int n : input) {
+    part1 += prng(n, LIMIT);
+  }
+  std::cout << "Part 1: " << part1 << std::endl;
+
+  int part2 = findBestScore(input);
+  std::cout << "Part 2: " << part2 << std::endl;
+
+  return 0;
+}