Brute-force solution to day 22 part 1.

2019/src/day22.cpp

@@ -1,31 +1,48 @@
 #include <iostream>
+#include <numeric>
 #include "days.hpp"
 #include "utils.hpp"
 
 void aoc2019::day22_part1(std::istream &input, std::ostream &output) {
-    std::int64_t increment = 1;
-    std::int64_t offset = 0;
+    constexpr int DECK_SIZE = 10007;
 
-    constexpr std::int64_t DECK_SIZE = 10007;
+    std::vector<int> deck(DECK_SIZE);
+    std::iota(deck.begin(), deck.end(), 0);
+
+    auto copy = deck;
 
     std::string buffer;
     while (std::getline(input, buffer)) {
         std::string_view line = buffer;
         if (!line.find("deal into new stack")) {
-            increment *= -1;
+            std::reverse(deck.begin(), deck.end());
         } else if (!line.find("deal with increment ")) {
-            std::int64_t new_increment;
+            int new_increment;
             from_chars(line.substr(20), new_increment);
-            increment *= new_increment;
-            increment %= DECK_SIZE;
+            int pos = 0;
+            for (auto value : deck) {
+                copy[pos] = value;
+                pos = (pos + new_increment) % DECK_SIZE;
+            }
+            std::swap(deck, copy);
         } else {
-            std::int64_t new_offset;
-            from_chars(line, new_offset);
-            offset += increment * new_offset;
-            offset %= DECK_SIZE;
+            // cut
+            int new_offset;
+            from_chars(line.substr(4), new_offset);
+            if (new_offset < 0) {
+                new_offset = DECK_SIZE + new_offset;
+            }
+
+            auto it = std::copy(deck.begin() + new_offset, deck.end(), copy.begin());
+            std::copy(deck.begin(), deck.begin() + new_offset, it);
+
+            std::swap(deck, copy);
         }
     }
-	output << "Not implemented\n";
+
+    auto location = std::find(deck.begin(), deck.end(), 2019);
+
+    output << std::distance(deck.begin(), location) << std::endl;
 }
 
 void aoc2019::day22_part2(std::istream &input, std::ostream &output) {