aoc 2024, day 8

1 files changed, 112 insertions, 0 deletions

diff --git a/2024/src/day08.cpp b/2024/src/day08.cpp
new file mode 100644
index 0000000..87e318d
--- /dev/null
+++ b/2024/src/day08.cpp
@@ -0,0 +1,112 @@
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <set>
+#include <string>
+#include <tuple>
+using namespace std;
+
+using pos_type = tuple<size_t, size_t>;
+
+map<pos_type, char>
+read_file(string_view filename)
+{
+        fstream             input{ filename };
+        map<pos_type, char> data;
+
+        size_t yPos = 0;
+        for ( string line; getline(input, line); ) {
+                for ( size_t xPos = 0; xPos != line.size(); ++xPos ) {
+                        data[{ xPos, yPos }] = line[xPos];
+                }
+                ++yPos;
+        }
+
+        return data;
+}
+
+void
+part1(const map<pos_type, char>& data)
+{
+        map<char, vector<pos_type>> unique_frequencies;
+        for ( const auto& [position, frequency]: data ) {
+                if ( frequency == '.' ) {
+                        continue;
+                }
+                unique_frequencies[frequency].emplace_back(position);
+        }
+
+        set<pos_type> antinodes;
+        for ( const auto& [frequency, positions]: unique_frequencies ) {
+                for ( size_t i = 0; i != positions.size(); ++i ) {
+                        for ( size_t j = i + 1; j != positions.size(); ++j ) {
+                                const auto [lhs_x, lhs_y] = positions[i];
+                                const auto [rhs_x, rhs_y] = positions[j];
+
+                                const auto delta_x = rhs_x - lhs_x;
+                                const auto delta_y = rhs_y - lhs_y;
+
+                                pos_type new_position1{ lhs_x - delta_x, lhs_y - delta_y };
+                                if ( data.contains(new_position1) ) {
+                                        antinodes.emplace(new_position1);
+                                }
+
+                                pos_type new_position2{ rhs_x + delta_x, rhs_y + delta_y };
+                                if ( data.contains(new_position2) ) {
+                                        antinodes.emplace(new_position2);
+                                }
+                        }
+                }
+        }
+        cout << antinodes.size() << endl;
+}
+
+void
+part2(const map<pos_type, char>& data)
+{
+        map<char, vector<pos_type>> unique_frequencies;
+        for ( const auto& [position, frequency]: data ) {
+                if ( frequency == '.' ) {
+                        continue;
+                }
+                unique_frequencies[frequency].emplace_back(position);
+        }
+
+        set<pos_type> antinodes;
+        for ( const auto& [frequency, positions]: unique_frequencies ) {
+                for ( size_t i = 0; i != positions.size(); ++i ) {
+                        for ( size_t j = i + 1; j != positions.size(); ++j ) {
+                                const auto [lhs_x, lhs_y] = positions[i];
+                                const auto [rhs_x, rhs_y] = positions[j];
+
+                                const auto delta_x = rhs_x - lhs_x;
+                                const auto delta_y = rhs_y - lhs_y;
+
+                                for ( size_t count = 0;; ++count ) {
+                                        pos_type new_position{ lhs_x - count * delta_x, lhs_y - count * delta_y };
+                                        if ( !data.contains(new_position) ) {
+                                                break;
+                                        }
+                                        antinodes.emplace(new_position);
+                                }
+
+                                for ( size_t count = 0;; ++count ) {
+                                        pos_type new_position{ rhs_x + count * delta_x, rhs_y + count * delta_y };
+                                        if ( !data.contains(new_position) ) {
+                                                break;
+                                        }
+                                        antinodes.emplace(new_position);
+                                }
+                        }
+                }
+        }
+        cout << antinodes.size() << endl;
+}
+
+int
+main()
+{
+        auto data = read_file("data/day08.txt");
+        part1(data);
+        part2(data);
+}