aoc 2016, days 4, 5, 6

4 files changed, 231 insertions, 0 deletions

diff --git a/2016/src/day04.cpp b/2016/src/day04.cpp
new file mode 100644
index 0000000..713b16f
--- /dev/null
+++ b/2016/src/day04.cpp
@@ -0,0 +1,102 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <set>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+split(const string& line, const regex& sep)
+{
+        return { sregex_token_iterator(line.begin(), line.end(), sep, -1), {} };
+}
+
+vector<tuple<vector<string>, long, string>>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+
+        vector<tuple<vector<string>, long, string>> result;
+
+        for ( string line; getline(input, line); ) {
+                static const regex sep{ "[\\[\\]-]" };
+
+                auto parts = split(line, sep);
+
+                auto checksum = parts.at(parts.size() - 1);
+                parts.pop_back();
+
+                auto selector = stol(parts.at(parts.size() - 1));
+                parts.pop_back();
+
+                result.emplace_back(parts, selector, checksum);
+        }
+
+        return result;
+}
+
+void
+part1(const vector<tuple<vector<string>, long, string>>& data)
+{
+        long sum = 0;
+        for ( const auto& [ids, selector, checksum]: data ) {
+                map<char, long> counts;
+                for ( const auto& id: ids ) {
+                        for ( const auto chr: id ) {
+                                ++counts[chr];
+                        }
+                }
+
+                set<tuple<long, char>> tops;
+                for ( const auto& [chr, count]: counts ) {
+                        tops.emplace(-count, chr);
+                }
+
+                string result;
+                for ( const auto& [count, chr]: tops ) {
+                        result += chr;
+                }
+
+                if ( result.starts_with(checksum) ) {
+                        sum += selector;
+                }
+        }
+        cout << sum << endl;
+}
+
+void
+part2(const vector<tuple<vector<string>, long, string>>& lines)
+{
+        auto rot = [](string str, int n) {
+                for ( auto& chr: str ) {
+                        chr = ((chr - 'a' + n) % 26) + 'a';
+                }
+                return str;
+        };
+
+        auto is_northpole = [&](const string& str, int n) {
+                return rot(str, n) == "northpole";
+        };
+
+        for ( const auto& line: lines ) {
+                const auto& ids      = get<0>(line);
+                const auto  selector = get<1>(line);
+                if ( ranges::any_of(ids, [&](auto& str) { return is_northpole(str, (int) selector); }) ) {
+                        cout << selector << endl;
+                        return;
+                }
+        }
+}
+
+int
+main()
+{
+        auto data = read_file("data/day04.txt");
+        part1(data);
+        part2(data);
+}
diff --git a/2016/src/day05.cpp b/2016/src/day05.cpp
new file mode 100644
index 0000000..dfce653
--- /dev/null
+++ b/2016/src/day05.cpp
@@ -0,0 +1,74 @@
+// Standard C++
+#include <array>
+#include <fstream>
+#include <iostream>
+#include <string>
+
+// Standard C
+#include <cstdlib> // memcmp
+
+// System
+#include <md5.h>
+
+using namespace std;
+
+void
+part1(string_view puzzle)
+{
+        array<char, MD5_DIGEST_STRING_LENGTH> digest{};
+
+        string result;
+
+        string input;
+        for ( unsigned long counter = 0;; ++counter ) {
+                input = puzzle;
+                input += to_string(counter);
+                MD5Data(input.data(), input.size(), digest.data());
+
+                if ( memcmp(digest.data(), "00000", 5) == 0 ) {
+                        result += digest.at(5);
+                        if ( result.length() == 8 ) {
+                                cout << result << endl;
+                                return;
+                        }
+                }
+        }
+}
+
+void
+part2(string_view puzzle)
+{
+        array<char, MD5_DIGEST_STRING_LENGTH> digest{};
+
+        string result = "________";
+
+        string input;
+        for ( unsigned long counter = 0;; ++counter ) {
+                input = puzzle;
+                input += to_string(counter);
+                MD5Data(input.data(), input.size(), digest.data());
+
+                if ( memcmp(digest.data(), "00000", 5) == 0 ) {
+                        auto position = digest.at(5) - '0';
+                        if ( position < 0 || position > 7 ) {
+                                continue;
+                        }
+                        if ( result.at(size_t(position)) != '_' ) {
+                                continue;
+                        }
+                        result.at(size_t(position)) = digest.at(6);
+                        if ( result.find('_') == string::npos ) {
+                                cout << result << endl;
+                                return;
+                        }
+                }
+        }
+}
+
+int
+main()
+{
+        auto puzzle = "reyedfim"s;
+        part1(puzzle);
+        part2(puzzle);
+}
diff --git a/2016/src/day06.cpp b/2016/src/day06.cpp
new file mode 100644
index 0000000..5bd0f93
--- /dev/null
+++ b/2016/src/day06.cpp
@@ -0,0 +1,52 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <regex>
+#include <set>
+#include <sstream>
+#include <string>
+#include <tuple>
+#include <vector>
+
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+        fstream input{ filename };
+
+        vector<string> lines;
+
+        for ( string line; getline(input, line); ) {
+                lines.emplace_back(line);
+        }
+
+        return lines;
+}
+
+void
+solve(const vector<string>& lines)
+{
+        string part1;
+        string part2;
+
+        for ( size_t col = 0; col != lines[0].length(); ++col ) {
+                map<char, size_t> counts;
+                for ( const auto& line: lines ) {
+                        ++counts[line[col]];
+                }
+
+                part1 += max_element(counts.begin(), counts.end(), [](auto lhs, auto rhs) { return lhs.second < rhs.second; })->first;
+                part2 += min_element(counts.begin(), counts.end(), [](auto lhs, auto rhs) { return lhs.second < rhs.second; })->first;
+        }
+
+        cout << part1 << '\n'
+             << part2 << endl;
+}
+
+int
+main()
+{
+        auto lines = read_file("data/day06.txt");
+        solve(lines);
+}
diff --git a/makefile b/makefile
index 5ce2c9a..ffd0a23 100644
--- a/makefile
+++ b/makefile
@@ -21,6 +21,9 @@ all: $(patsubst 2015/src/%.cpp,2015/bin/%,$(wildcard 2015/src/*.cpp)) \
 2016/bin/%: 2016/src/%.cpp | 2016/bin
         c++ $(CPPFLAGS) $^ -o $@
 
+2016/bin/day05: 2016/src/day05.cpp | 2016/bin
+        c++ $(CPPFLAGS) $^ -lmd -o $@
+
 # 2020
 2020/bin/%: 2020/src/%.cpp | 2020/bin
         c++ $(CPPFLAGS) $^ -o $@