aoc 2015, day 18

1 files changed, 143 insertions, 0 deletions

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);
+}