Add 2022 Day 3.

.idea/dictionaries/mgrettondann.xml

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+<component name="ProjectDictionaryState">
+  <dictionary name="mgrettondann" />
+</component>

2022/puzzle-03-01.cc

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+//
+// Created by Matthew Gretton-Dann on 02/12/2022.
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <iostream>
+#include <map>
+#include <string>
+
+using Int = std::int64_t;
+
+auto main() -> int
+{
+  std::string letters{" abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"};
+
+  Int score{0};
+  std::string line;
+  while (std::getline(std::cin, line)) {
+    auto left{line.substr(0, line.size() / 2)};
+    auto right{line.substr(line.size() / 2)};
+    std::sort(left.begin(), left.end());
+        std::sort(right.begin(), right.end());
+    std::string result;
+    std::set_intersection(left.begin(), left.end(), right.begin(), right.end(),
+                          std::back_inserter(result));
+    assert(!result.empty());
+    score += letters.find(result[0]);
+  }
+  std::cout << "Score: " << score << '\n';
+  return EXIT_SUCCESS;
+}

2022/puzzle-03-02.cc

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+//
+// Created by Matthew Gretton-Dann on 02/12/2022.
+//
+
+#include <algorithm>
+#include <cstdlib>
+#include <iostream>
+#include <map>
+#include <string>
+
+using Int = std::int64_t;
+
+auto main() -> int
+{
+  std::string letters{" abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"};
+
+  Int score{0};
+  std::string line;
+  Int state{0};
+  std::string current;
+  while (std::getline(std::cin, line)) {
+    std::sort(line.begin(), line.end());
+    if (state == 0) {
+      current = line;
+      ++state;
+    }
+    else if (state == 1) {
+      std::string r;
+      std::set_intersection(current.begin(), current.end(), line.begin(), line.end(),
+                            std::back_inserter(r));
+      current = r;
+      ++state;
+    }
+    else if (state == 2) {
+      std::string r;
+      std::set_intersection(current.begin(), current.end(), line.begin(), line.end(),
+                            std::back_inserter(r));
+      state = 0;
+      assert(!r.empty());
+      score += letters.find(r[0]);
+    }
+  }
+  assert(state == 0);
+  std::cout << "Score: " << score << '\n';
+  return EXIT_SUCCESS;
+}