From 2cbb07b60558213cffc5db36bbd9276ef21709ca Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 8 Dec 2024 12:30:47 +0100
Subject: aoc 2024, day 8

---
 2024/src/day08.cpp | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)
 create mode 100644 2024/src/day08.cpp

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);
+}
-- 
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