day 14, aoc 2016

1 files changed, 121 insertions, 0 deletions

diff --git a/2016/src/day14.cpp b/2016/src/day14.cpp
new file mode 100644
index 0000000..a9be56c
--- /dev/null
+++ b/2016/src/day14.cpp
@@ -0,0 +1,121 @@
+// Standard C++
+#include <array>
+#include <iostream>
+#include <map>
+#include <optional>
+#include <string>
+
+// Standard C
+#include <cstring>
+
+// System
+#include <md5.h>
+
+using namespace std;
+
+namespace {
+
+optional<char>
+contains_repeating_chars(string_view str)
+{
+        for ( size_t i = 2; i < str.size(); ++i ) {
+                if ( str[i] == str[i - 1] && str[i] == str[i - 2] ) {
+                        return str[i];
+                }
+        }
+
+        return {};
+}
+
+string
+md5(const string& input)
+{
+        array<char, MD5_DIGEST_STRING_LENGTH> digest{};
+        MD5Data(input.data(), input.size(), digest.data());
+        return digest.data();
+}
+
+int
+solve(const function<string(int)>& get_hash)
+{
+        int keys = 0;
+
+        for ( int index = 0;; ++index ) {
+                auto hash = get_hash(index);
+
+                auto repeat = contains_repeating_chars(hash);
+
+                if ( !repeat.has_value() ) {
+                        continue;
+                }
+
+                const string pattern(5, repeat.value());
+
+                for ( auto index2 = index + 1; index2 != index + 1000; ++index2 ) {
+                        hash = get_hash(index2);
+                        if ( hash.find(pattern) != string::npos ) {
+                                ++keys;
+                                break;
+                        }
+                }
+
+                if ( keys == 64 ) {
+                        return index;
+                }
+        }
+}
+
+void
+part1(const string& input)
+{
+        map<int, string> cache;
+
+        auto get_hash = [&](int index) {
+                if ( cache.contains(index) ) {
+                        return cache.at(index);
+                }
+
+                auto hash = md5(input + to_string(index));
+
+                cache.emplace(index, hash);
+
+                return hash;
+        };
+
+        cout << solve(get_hash) << '\n';
+}
+
+void
+part2(const string& input)
+{
+        map<int, string> cache;
+
+        auto get_hash = [&](int index) {
+                if ( cache.contains(index) ) {
+                        return cache.at(index);
+                }
+
+                auto hash = input + to_string(index);
+
+                for ( int i = 0; i != 2017; ++i ) {
+                        hash = md5(hash);
+                }
+
+                cache.emplace(index, hash);
+
+                return hash;
+        };
+
+        cout << solve(get_hash) << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        // part1("abc");
+        // part2("abc");
+        part1("qzyelonm");
+        part2("qzyelonm");
+}