Add 2021 day 10 puzzles

2021/puzzle-10-01.cc

@@ -0,0 +1,40 @@
+//
+// Created by Matthew Gretton-Dann on 10/12/2021.
+//
+
+#include <cassert>
+#include <iostream>
+#include <map>
+#include <stack>
+#include <string>
+
+auto main() -> int
+{
+  std::map<char, char> matches{{'(', ')'}, {'[', ']'}, {'{', '}'}, {'<', '>'}};
+  std::map<char, unsigned> scores{{')', 3}, {']', 57}, {'}', 1197}, {'>', 25137}};
+
+  std::string line;
+  unsigned score{0};
+  while (std::getline(std::cin, line)) {
+    std::stack<char> expecting;
+    for (auto c : line) {
+      if (auto it = matches.find(c); it != matches.end()) {
+        expecting.push(it->second);
+      }
+      else if (!expecting.empty()) {
+        if (c == expecting.top()) {
+          expecting.pop();
+        }
+        else {
+          auto score_it{scores.find(c)};
+          assert(score_it != scores.end());
+          score += score_it->second;
+          break;
+        }
+      }
+    }
+  }
+
+  std::cout << "Total score: " << score << '\n';
+  return 0;
+}

2021/puzzle-10-02.cc

@@ -0,0 +1,59 @@
+//
+// Created by Matthew Gretton-Dann on 10/12/2021.
+//
+
+#include <cassert>
+#include <iostream>
+#include <map>
+#include <stack>
+#include <string>
+#include <vector>
+
+auto main() -> int
+{
+  std::map<char, char> matches{{'(', ')'}, {'[', ']'}, {'{', '}'}, {'<', '>'}};
+  std::map<char, unsigned> scores{{')', 1}, {']', 2}, {'}', 3}, {'>', 4}};
+
+  std::string line;
+  std::vector<std::uint64_t> line_scores;
+  while (std::getline(std::cin, line)) {
+    bool incomplete{true};
+    std::stack<char> expecting;
+    for (auto c : line) {
+      if (auto it = matches.find(c); it != matches.end()) {
+        expecting.push(it->second);
+      }
+      else if (!expecting.empty()) {
+        if (c == expecting.top()) {
+          expecting.pop();
+        }
+        else {
+          incomplete = false;
+          break;
+        }
+      }
+      else {
+        abort();
+      }
+    }
+
+    if (!incomplete) {
+      continue;
+    }
+
+    // expecting has the characters we expect.
+    std::uint64_t score{0};
+    while (!expecting.empty()) {
+      score *= 5;
+      auto score_it{scores.find(expecting.top())};
+      assert(score_it != scores.end());
+      score += score_it->second;
+      expecting.pop();
+    }
+    line_scores.push_back(score);
+  }
+
+  std::sort(line_scores.begin(), line_scores.end());
+  std::cout << "Middle score: " << line_scores.at(line_scores.size() / 2) << '\n';
+  return 0;
+}