Add 2016 day 1 puzzles.

2016/puzzle-01-01.cc

@@ -0,0 +1,69 @@
+//
+// Created by Matthew Gretton-Dann on 02/12/2021.
+//
+
+#include <iostream>
+#include <string>
+
+enum Direction { north, east, south, west };
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Failed to read line.\n";
+    return 1;
+  }
+
+  Direction direction{north};
+  int horiz{0};
+  int vert{0};
+  for (std::size_t pos{0}; pos < line.size(); pos += 2) {
+    switch (line.at(pos)) {
+    case 'L':
+      if (direction == Direction::north) {
+        direction = Direction::west;
+      }
+      else {
+        direction = static_cast<Direction>(static_cast<int>(direction) - 1);
+      }
+      break;
+    case 'R':
+      if (direction == Direction::west) {
+        direction = Direction::north;
+      }
+      else {
+        direction = static_cast<Direction>(static_cast<int>(direction) + 1);
+      }
+      break;
+    default:
+      abort();
+    }
+    ++pos;
+    assert(pos < line.size());
+    std::size_t idx{0};
+    auto dist{static_cast<int>(std::stoul(line.substr(pos), &idx))};
+    pos += idx;
+    switch (direction) {
+    case Direction::north:
+      vert += dist;
+      break;
+    case Direction::east:
+      horiz += dist;
+      break;
+    case Direction::south:
+      vert -= dist;
+      break;
+    case Direction::west:
+      horiz -= dist;
+      break;
+    default:
+      abort();
+    }
+  }
+
+  horiz = std::abs(horiz);
+  vert = std::abs(vert);
+  std::cout << "We end up " << horiz << " + " << vert << " = " << horiz + vert << " blocks away.\n";
+  return 0;
+}

2016/puzzle-01-02.cc

@@ -0,0 +1,58 @@
+//
+// Created by Matthew Gretton-Dann on 02/12/2021.
+//
+
+#include <iostream>
+#include <set>
+#include <string>
+
+enum Direction { north, east, south, west };
+using Location = std::pair<int, int>;
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Failed to read line.\n";
+    return 1;
+  }
+
+  std::set<Location> visited;
+  Location current{0, 0};
+  Location direction{0, 1};
+  visited.insert(current);
+
+  for (std::size_t pos{0}; pos < line.size(); pos += 2) {
+    switch (line.at(pos)) {
+    case 'L':
+      direction = {-direction.second, direction.first};
+      break;
+    case 'R':
+      direction = {direction.second, -direction.first};
+      break;
+    default:
+      abort();
+    }
+
+    ++pos;
+    assert(pos < line.size());
+    std::size_t idx{0};
+    auto dist{static_cast<int>(std::stoul(line.substr(pos), &idx))};
+    while (dist-- > 0) {
+      current.first += direction.first;
+      current.second += direction.second;
+      if (visited.find(current) != visited.end()) {
+        auto horiz = std::abs(current.first);
+        auto vert = std::abs(current.second);
+        std::cout << "We end up " << horiz << " + " << vert << " = " << horiz + vert
+                  << " blocks away.\n";
+        return 0;
+      }
+      visited.insert(current);
+    }
+
+    pos += idx;
+  }
+  std::cerr << "Didn't find an answer.\n";
+  return 1;
+}