Add 2021 day 6 puzzles

2016/puzzle-09-01.cc

@@ -0,0 +1,59 @@
+//
+// Created by Matthew Gretton-Dann on 05/12/2021.
+//
+
+#include <iostream>
+#include <string>
+
+std::string decompress(std::string const& s)
+{
+  std::string result;
+  std::size_t idx{0};
+  while (idx < s.size()) {
+    if (s[idx] != '(') {
+      auto idx2{s.find('(', idx)};
+      if (idx2 == std::string::npos) {
+        idx2 = s.size();
+      };
+      result += s.substr(idx, idx2 - idx);
+      idx = idx2;
+    }
+    else {
+      assert(s[idx] == '(');
+      ++idx;
+      std::size_t end{0};
+      auto length{std::stoul(s.substr(idx), &end)};
+      idx += end;
+      assert(idx < s.size());
+      assert(s[idx] == 'x');
+      ++idx;
+      auto count{std::stoul(s.substr(idx), &end)};
+      idx += end;
+      assert(idx < s.size());
+      assert(s[idx] == ')');
+      ++idx;
+      assert(length <= s.size());
+      assert(idx <= s.size() - length);
+      while (count-- != 0) {
+        result += s.substr(idx, length);
+      }
+      idx += length;
+    }
+  }
+
+  return result;
+}
+
+auto main() -> int
+{
+  std::string line;
+  std::string input;
+
+  while (std::getline(std::cin, line)) {
+    input += line;
+  }
+  std::cout << input;
+  auto output{decompress(input)};
+  std::cout << "Output length: " << output.size() << '\n';
+  return 0;
+}

2016/puzzle-09-02.cc

@@ -0,0 +1,56 @@
+//
+// Created by Matthew Gretton-Dann on 05/12/2021.
+//
+
+#include <iostream>
+#include <string>
+
+std::size_t decompress_length(std::string const& s)
+{
+  std::size_t result_len{0};
+  std::size_t idx{0};
+  while (idx < s.size()) {
+    if (s[idx] != '(') {
+      auto idx2{s.find('(', idx)};
+      if (idx2 == std::string::npos) {
+        idx2 = s.size();
+      };
+      result_len += idx2 - idx;
+      idx = idx2;
+    }
+    else {
+      assert(s[idx] == '(');
+      ++idx;
+      std::size_t end{0};
+      auto length{std::stoul(s.substr(idx), &end)};
+      idx += end;
+      assert(idx < s.size());
+      assert(s[idx] == 'x');
+      ++idx;
+      auto count{std::stoul(s.substr(idx), &end)};
+      idx += end;
+      assert(idx < s.size());
+      assert(s[idx] == ')');
+      ++idx;
+      assert(length <= s.size());
+      assert(idx <= s.size() - length);
+      result_len += count * decompress_length(s.substr(idx, length));
+      idx += length;
+    }
+  }
+
+  return result_len;
+}
+
+auto main() -> int
+{
+  std::string line;
+  std::string input;
+
+  while (std::getline(std::cin, line)) {
+    input += line;
+  }
+  auto output{decompress_length(input)};
+  std::cout << "Output length: " << output << '\n';
+  return 0;
+}