Solution to day 21.

2019/src/day21.cpp

@@ -1,10 +1,47 @@
 #include <iostream>
 #include "days.hpp"
+#include "utils.hpp"
+
+namespace {
+    void solve(std::istream &input, std::string_view program, std::ostream &output) {
+        aoc2019::IntCodeComputer computer(input);
+        std::deque<std::int64_t> output_buffer;
+        computer.connectOutput(output_buffer);
+        computer.run();
+        output_buffer.clear();
+
+        computer.sendInputs(program);
+
+        computer.run();
+        if (output_buffer.back() < 127) {
+            for (char c : output_buffer) {
+                output << c;
+            }
+        } else {
+            output << output_buffer.back() << std::endl;
+        }
+    }
+}
 
 void aoc2019::day21_part1(std::istream &input, std::ostream &output) {
-	output << "Not implemented\n";
+    std::string_view program = "OR A J\n"  // Check if any of the next 3 places is a hole
+                               "AND B J\n"
+                               "AND C J\n"
+                               "NOT J J\n"
+                               "AND D J\n" // Jump if the landing space is clear
+                               "WALK\n";
+
+    solve(input, program, output);
 }
 
 void aoc2019::day21_part2(std::istream &input, std::ostream &output) {
-	output << "Not implemented\n";
+    std::string_view program = "NOT H J\n" // If you can safely jump twice
+                               "OR C J\n"  // And either of the next 3 places contains a hole
+                               "AND A J\n"
+                               "AND B J\n"
+                               "NOT J J\n"
+                               "AND D J\n" // And we can land our first jump, then jump.
+                               "RUN\n";
+
+    solve(input, program, output);
 }