Add 2016 day 14 puzzles

Author: matt-gretton-dann

2016/puzzle-14-01.CMakeLists.txt

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+find_package(OpenSSL REQUIRED)
+target_link_libraries("${puzzle_name}" OpenSSL::SSL)

2016/puzzle-14-01.cc

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+//
+// Created by Matthew Gretton-Dann on 06/12/2021.
+//
+
+#include <array>
+#include <iostream>
+#include <string>
+#include <string_view>
+
+#include <openssl/evp.h>
+
+using MD5Digest = std::array<unsigned char, EVP_MAX_MD_SIZE>;
+
+auto md5(std::string const& s) -> std::string
+{
+  MD5Digest digest;
+  EVP_MD const* md{EVP_md5()};
+  unsigned int md_len{0};
+
+  EVP_MD_CTX* md_context{EVP_MD_CTX_new()};
+  assert(md_context != nullptr);
+  EVP_DigestInit_ex2(md_context, md, nullptr);
+  EVP_DigestUpdate(md_context, s.data(), s.length());
+  EVP_DigestFinal_ex(md_context, digest.data(), &md_len);
+  std::string result;
+  static std::string_view letters{"0123456789abcdef"};
+  for (auto i{0}; i < md_len; ++i) {
+    result += letters[(digest[i] & 0xf0) >> 4];
+    result += letters[(digest[i] & 0xf)];
+  }
+  return result;
+}
+
+auto has_three_char_sequence(std::string const& s) -> char
+{
+  std::string result;
+  for (std::size_t idx{0}; idx < s.size() - 2; ++idx) {
+    if (s[idx] == s[idx + 1] && s[idx] == s[idx + 2]) {
+      return s[idx];
+    }
+  }
+  return '\0';
+}
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Failed to read line\n";
+    return 1;
+  }
+
+  unsigned codes_seen{0};
+  unsigned index{0};
+  while (codes_seen != 64) {
+    std::string code{line};
+    code += std::to_string(index);
+    auto md5sum{md5(code)};
+    char c{has_three_char_sequence(md5sum)};
+    if (c != '\0') {
+      bool success{false};
+      std::string s(5, c);
+      for (unsigned i2 = index + 1; i2 < index + 1001; ++i2) {
+        std::string code2{line};
+        code2 += std::to_string(i2);
+        auto md5sum2{md5(code2)};
+        success = md5sum2.find(s) != std::string::npos;
+        if (success) {
+          break;
+        }
+      }
+      if (success) {
+        std::cout << "Code " << codes_seen << " at index " << index << '\n';
+        ++codes_seen;
+      }
+    }
+    ++index;
+  }
+
+  std::cout << "Index " << index - 1 << '\n';
+  return 0;
+}

2016/puzzle-14-02.CMakeLists.txt

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+find_package(OpenSSL REQUIRED)
+target_link_libraries("${puzzle_name}" OpenSSL::SSL)

2016/puzzle-14-02.cc

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+//
+// Created by Matthew Gretton-Dann on 06/12/2021.
+//
+
+#include <array>
+#include <iostream>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include <openssl/evp.h>
+
+using MD5Digest = std::array<unsigned char, EVP_MAX_MD_SIZE>;
+
+auto md5(std::string const& s) -> std::string
+{
+  MD5Digest digest;
+  EVP_MD const* md{EVP_md5()};
+  unsigned int md_len{0};
+
+  EVP_MD_CTX* md_context{EVP_MD_CTX_new()};
+  assert(md_context != nullptr);
+  EVP_DigestInit_ex2(md_context, md, nullptr);
+  EVP_DigestUpdate(md_context, s.data(), s.length());
+  EVP_DigestFinal_ex(md_context, digest.data(), &md_len);
+  std::string result;
+  static std::string_view letters{"0123456789abcdef"};
+  for (auto i{0}; i < md_len; ++i) {
+    result += letters[(digest[i] & 0xf0) >> 4];
+    result += letters[(digest[i] & 0xf)];
+  }
+  return result;
+}
+
+auto key_stretch(std::string const& s) -> std::string
+{
+  std::string r{s};
+  for (unsigned i = 0; i < 2017; ++i) {
+    r = md5(r);
+  }
+  return r;
+}
+
+struct Cache
+{
+  explicit Cache(std::string const& key) : key_(key) {}
+
+  auto md5(unsigned index) -> std::string
+  {
+    while (index >= cache_.size()) {
+      cache_.push_back(key_stretch(key_ + std::to_string(index)));
+    }
+    return cache_[index];
+  }
+
+  std::string key_;
+  std::vector<std::string> cache_;
+};
+
+auto has_three_char_sequence(std::string const& s) -> char
+{
+  std::string result;
+  for (std::size_t idx{0}; idx < s.size() - 2; ++idx) {
+    if (s[idx] == s[idx + 1] && s[idx] == s[idx + 2]) {
+      return s[idx];
+    }
+  }
+  return '\0';
+}
+
+auto main() -> int
+{
+  std::string line;
+  if (!std::getline(std::cin, line)) {
+    std::cerr << "Failed to read line\n";
+    return 1;
+  }
+
+  Cache cache{line};
+  unsigned codes_seen{0};
+  unsigned index{0};
+  while (codes_seen != 64) {
+    auto md5sum{cache.md5(index)};
+    char c{has_three_char_sequence(md5sum)};
+    if (c != '\0') {
+      bool success{false};
+      std::string s(5, c);
+      for (unsigned i2 = index + 1; i2 < index + 1001; ++i2) {
+        std::string code2{line};
+        code2 += std::to_string(i2);
+        auto md5sum2{cache.md5(i2)};
+        success = md5sum2.find(s) != std::string::npos;
+        if (success) {
+          break;
+        }
+      }
+      if (success) {
+        std::cout << "Code " << codes_seen << " at index " << index << " letter " << c << " hash "
+                  << cache.md5(index) << '\n';
+        ++codes_seen;
+      }
+    }
+    ++index;
+  }
+
+  std::cout << "Index " << index - 1 << '\n';
+  return 0;
+}