1 files changed, 135 insertions, 0 deletions

diff --git a/2018/src/day04.cpp b/2018/src/day04.cpp
new file mode 100644
index 0000000..ea3c69f
--- /dev/null
+++ b/2018/src/day04.cpp
@@ -0,0 +1,135 @@
+#include <algorithm>
+#include <filesystem>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <string>
+#include <vector>
+
+using namespace std;
+
+namespace {
+
+struct Record {
+        int  guard_id;
+        long start_sleep;
+        long stop_sleep;
+};
+
+long
+to_timestamp(const string& line)
+{
+        long year = stol(line.substr(1, 4));
+        long mon  = stol(line.substr(6, 2));
+        long day  = stol(line.substr(9, 2));
+        long hour = stol(line.substr(12, 2));
+        long min  = stol(line.substr(15, 2));
+
+        auto timestamp = (year * 100'000'000) + (mon * 1'000'000) + (day * 10'000) + (hour * 100) + min; // NOLINT
+
+        return timestamp;
+}
+
+vector<Record>
+read_file(const filesystem::path& filename)
+{
+        ifstream       file{ filename };
+        vector<string> lines;
+
+        for ( string line; getline(file, line); ) {
+                lines.emplace_back(line);
+        }
+
+        ranges::sort(lines);
+
+        vector<Record> records;
+
+        int  guard       = -1;
+        long start_sleep = -1;
+        long stop_sleep  = -1;
+        for ( const auto& line: lines ) {
+                if ( line.find(" Guard #") != string::npos ) {
+                        guard = stoi(line.substr(26));
+                }
+                else if ( line.find(" falls asleep") != string::npos ) {
+                        start_sleep = to_timestamp(line);
+                }
+                else if ( line.find(" wakes up") != string::npos ) {
+                        stop_sleep = to_timestamp(line);
+                        records.emplace_back(guard, start_sleep, stop_sleep);
+                }
+        }
+
+        return records;
+}
+
+void
+part1(const vector<Record>& records)
+{
+        map<int, long> sleep_amounts;
+
+        for ( const auto& record: records ) {
+                sleep_amounts[record.guard_id] += record.stop_sleep - record.start_sleep;
+        }
+
+        auto max_amount = ranges::max_element(sleep_amounts,
+                                              [](const auto& lhs, const auto& rhs) {
+                                                      return lhs.second < rhs.second;
+                                              });
+
+        map<long, unsigned> sleep_counts;
+
+        for ( const auto& record: records ) {
+                if ( record.guard_id != max_amount->first ) {
+                        continue;
+                }
+
+                for ( auto timestamp = record.start_sleep; timestamp != record.stop_sleep; ++timestamp ) {
+                        sleep_counts[timestamp % 10'000]++;
+                }
+        }
+
+        auto max_count = ranges::max_element(sleep_counts,
+                                             [](const auto& lhs, const auto& rhs) {
+                                                     return lhs.second < rhs.second;
+                                             });
+
+        cout << "Part 1: " << max_amount->first * (max_count->first % 100) << '\n';
+}
+
+void
+part2(const vector<Record>& records)
+{
+        map<int, map<long, unsigned>> sleep_counts;
+
+        for ( const auto& record: records ) {
+                for ( auto timestamp = record.start_sleep; timestamp != record.stop_sleep; ++timestamp ) {
+                        sleep_counts[record.guard_id][timestamp % 10'000]++;
+                }
+        }
+
+        int      found_guard = -1;
+        long     found_min   = -1;
+        unsigned max_count   = 0;
+        for ( const auto& [id, times]: sleep_counts ) {
+                for ( const auto& [min, count]: times ) {
+                        if ( count > max_count ) {
+                                max_count   = count;
+                                found_guard = id;
+                                found_min   = min % 100;
+                        }
+                }
+        }
+
+        cout << "Part 2: " << found_guard * found_min << '\n';
+}
+
+} // namespace
+
+int
+main()
+{
+        auto records = read_file("data/day04.txt");
+        part1(records);
+        part2(records);
+}