From 0413a04a422e5985ae91a02489cafcb85515ea9f Mon Sep 17 00:00:00 2001
From: Thomas Schmucker <ts@its1.de>
Date: Sun, 17 Nov 2024 16:59:53 +0100
Subject: aoc 2015, day 18

---
 2015/src/day18.cpp | 143 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)
 create mode 100644 2015/src/day18.cpp

(limited to '2015')

diff --git a/2015/src/day18.cpp b/2015/src/day18.cpp
new file mode 100644
index 0000000..fa465f4
--- /dev/null
+++ b/2015/src/day18.cpp
@@ -0,0 +1,143 @@
+#include <algorithm>
+#include <fstream>
+#include <iostream>
+#include <map>
+#include <tuple>
+using namespace std;
+
+using puzzle_type = map<tuple<size_t, size_t>, bool>;
+
+auto
+read_file(string_view filename)
+{
+	fstream     input{ filename };
+	puzzle_type puzzle;
+
+	size_t line = 0;
+	for ( string str; getline(input, str); ) {
+		for ( size_t column = 0; column != str.size(); ++column ) {
+			if ( str[column] == '#' ) {
+				puzzle[{ column, line }] = true;
+			}
+		}
+
+		++line;
+	}
+
+	return puzzle;
+}
+
+void
+iterate(puzzle_type& puzzle, size_t width)
+{
+	puzzle_type next;
+
+	for ( size_t line = 0; line != width; ++line ) {
+		for ( size_t column = 0; column != width; ++column ) {
+			static const vector<tuple<size_t, size_t>> offsets = {
+				{ -1, -1 },
+				{ 0, -1 },
+				{ 1, -1 },
+				{ -1, 0 },
+				{ 1, 0 },
+				{ -1, 1 },
+				{ 0, 1 },
+				{ 1, 1 }
+			};
+
+			size_t count = 0;
+			for ( const auto& [delta_x, delta_y]: offsets ) {
+				if ( puzzle[{ column + delta_x, line + delta_y }] ) {
+					++count;
+				}
+			}
+
+			if ( puzzle[{ column, line }] ) {
+				if ( count == 2 || count == 3 ) {
+					next[{ column, line }] = true;
+				}
+			}
+			else {
+				if ( count == 3 ) {
+					next[{ column, line }] = true;
+				}
+			}
+		}
+	}
+
+	puzzle.swap(next);
+}
+
+void
+print(puzzle_type puzzle, size_t width)
+{
+	for ( size_t line = 0; line != width; ++line ) {
+		for ( size_t column = 0; column != width; ++column ) {
+			auto value = puzzle[{ column, line }];
+			cout << (value ? '#' : '.');
+		}
+		cout << '\n';
+	}
+	cout << endl;
+}
+
+void
+part1(puzzle_type puzzle)
+{
+	static const size_t width = 100;
+
+	for ( int i = 0; i != 100; ++i ) {
+		iterate(puzzle, width);
+	}
+
+	long sum = 0;
+	for ( size_t line = 0; line != width; ++line ) {
+		for ( size_t column = 0; column != width; ++column ) {
+			auto value = puzzle[{ column, line }];
+			if ( value ) {
+				++sum;
+			}
+		}
+	}
+	cout << sum << endl;
+}
+
+void
+enable_corners(puzzle_type& puzzle, size_t width)
+{
+	puzzle[{ 0, 0 }]                 = true;
+	puzzle[{ width - 1, 0 }]         = true;
+	puzzle[{ 0, width - 1 }]         = true;
+	puzzle[{ width - 1, width - 1 }] = true;
+}
+
+void
+part2(puzzle_type puzzle)
+{
+	static const size_t width = 100;
+
+	for ( int i = 0; i != 100; ++i ) {
+		enable_corners(puzzle, width);
+		iterate(puzzle, width);
+	}
+	enable_corners(puzzle, width);
+
+	long sum = 0;
+	for ( size_t line = 0; line != width; ++line ) {
+		for ( size_t column = 0; column != width; ++column ) {
+			auto value = puzzle[{ column, line }];
+			if ( value ) {
+				++sum;
+			}
+		}
+	}
+	cout << sum << endl;
+}
+
+int
+main()
+{
+	auto puzzle = read_file("data/day18.txt");
+	part1(puzzle);
+	part2(puzzle);
+}
-- 
cgit v1.3