From 56e890cec0a28c0a485212ccebfaf774235a79a2 Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Wed, 3 Jan 2024 23:35:54 +0100
Subject: prepare for more puzzles ... :)

---
 2023/src/day11.cpp | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)
 create mode 100644 2023/src/day11.cpp

(limited to '2023/src/day11.cpp')

diff --git a/2023/src/day11.cpp b/2023/src/day11.cpp
new file mode 100644
index 0000000..e1a0882
--- /dev/null
+++ b/2023/src/day11.cpp
@@ -0,0 +1,100 @@
+#include <cmath>
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <string>
+#include <vector>
+using namespace std;
+
+vector<string>
+read_file(string_view filename)
+{
+	fstream        input{ filename };
+	vector<string> data;
+
+	for ( string line; getline(input, line); ) {
+		data.emplace_back(line);
+	}
+
+	return data;
+}
+
+vector<tuple<long, long>>
+find_points(const vector<string>& input)
+{
+	vector<tuple<long, long>> result;
+
+	for ( size_t row = 0; row != input.size(); ++row ) {
+		const auto& line = input[row];
+
+		for ( size_t col = 0; col != line.size(); ++col ) {
+			if ( line[col] == '#' ) {
+				result.emplace_back(long(row), long(col));
+			}
+		}
+	}
+
+	return result;
+}
+
+void
+find_empty_rows_and_cols(const vector<string>& input, set<long>& cols, set<long>& rows)
+{
+	for ( size_t row = 0; row != input.size(); ++row ) {
+		const auto& line = input[row];
+		if ( line.find('#') == line.npos ) {
+			rows.insert(long(row));
+		}
+	}
+
+	for ( size_t col = 0; col != input[0].size(); ++col ) {
+		bool empty_col = true;
+		for ( const auto& line: input ) {
+			if ( line[col] == '#' ) {
+				empty_col = false;
+			}
+		}
+		if ( empty_col ) {
+			cols.insert(long(col));
+		}
+	}
+}
+
+long
+solve(const vector<string>& input, long scale)
+{
+	auto points = find_points(input);
+
+	set<long> cols;
+	set<long> rows;
+
+	find_empty_rows_and_cols(input, cols, rows);
+
+	for ( auto& point: points ) {
+		const auto row = get<0>(point) + count_if(rows.begin(), rows.end(), [&](long row) { return row < get<0>(point); }) * (scale - 1);
+		const auto col = get<1>(point) + count_if(cols.begin(), cols.end(), [&](long col) { return col < get<1>(point); }) * (scale - 1);
+
+		point = { row, col };
+	}
+
+	auto sum = 0L;
+	for ( size_t i = 0; i != points.size(); ++i ) {
+		for ( size_t j = i + 1; j != points.size(); ++j ) {
+			const auto& from = points[i];
+			const auto& to   = points[j];
+
+			sum += abs(get<0>(from) - get<0>(to)) + abs(get<1>(from) - get<1>(to));
+		}
+	}
+
+	return sum;
+}
+
+int
+main()
+{
+	const auto input = read_file("data/day11.txt");
+
+	cout << "Part1: " << solve(input, 2) << endl;
+	cout << "Part2: " << solve(input, 1000000) << endl;
+}
-- 
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