solve: year 2024 day 8 in ruby

Author: nguyenhuuit

2024/day8/input.txt

@@ -0,0 +1,50 @@
+..............U.............c.....3...............
+.....p.........F..................................
+.....m..7....................4x............3......
+..e.............F..........c...YH..3..............
+.......e...................................c..E..8
+................a...U................8............
+..............................4.F...8....x........
+............7.....4............Hc..E.......x......
+........p..............................E..........
+.............U.e....................x....t........
+.7..........................Z.H....g..............
+.........7..m.....S.........................E.....
+...F.....p...........6...SY.......................
+.................6..k...................g.........
+..........m......a........................g.......
+.......M.......................................g..
+..............a............Y....C........H........
+....u.......6........a.........C.GY...............
+.....M..................S......................2..
+..........M........S.....................2........
+........M.......................5.........z..f....
+.....................................Z........t.2.
+..........6.......................................
+......................................G...........
+.........................A.........G9....Z........
+........................C.........................
+.....k......................G......z..t...........
+.......k......................zs....f........5...9
+................h........................9....2...
+.............h.....0...........f.....K..ZX........
+..................................f...............
+.......1....................9.........Xz..........
+...............1......B.s......X..................
+............h...............B.....................
+..T.........k..................b..................
+...............u..................................
+.........u.............h..................0.......
+..............y...................................
+...............................t....X......5......
+.................A............................5...
+................u..................s..............
+.T..........b....y................................
+............y............................K........
+..1...............................s....B..........
+..............Ay.............B...P................
+..........T.......................K...........0...
+.............T..................P.........K.......
+......A....P......................................
+....b.........1...................................
+.........b................................P.......

2024/day8/part1.rb

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+def print_city_map(city_map, antinodes)
+  antinodes.each do |x, y|
+    city_map[x][y] = '#' if city_map[x][y] == '.'
+  end
+  puts city_map.map(&:join).join("\n")
+end
+
+def inside?(point, city_map)
+  x, y = point
+  height = city_map.length
+  width = city_map[0].length
+  x.between?(0, height - 1) && y.between?(0, width - 1)
+end
+
+def count_antenna(city_map)
+  city_map.each_with_index.with_object(Hash.new { |h, k| h[k] = [] }) do |(line, i), rs|
+    line.each_with_index do |cell, j|
+      rs[cell] << [i, j] unless cell == '.'
+    end
+  end
+end
+
+def solution(input)
+  city_map = input.split("\n").map(&:chars)
+  antennas = count_antenna(city_map)
+  antinodes = Set.new
+
+  antennas.each_value do |positions|
+    positions.combination(2).each do |p1, p2|
+      dx, dy = p1[0] - p2[0], p1[1] - p2[1]
+
+      p1_side = [p1[0] + dx, p1[1] + dy]
+      p2_side = [p2[0] - dx, p2[1] - dy]
+
+      antinodes.add(p1_side) if inside?(p1_side, city_map)
+      antinodes.add(p2_side) if inside?(p2_side, city_map)
+    end
+  end
+
+  print_city_map(city_map, antinodes)
+  antinodes.size
+end

2024/day8/part2.rb

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+def print_city_map(city_map, antinodes)
+  antinodes.each do |x, y|
+    city_map[x][y] = '#' if city_map[x][y] == '.'
+  end
+  puts city_map.map(&:join).join("\n")
+end
+
+def inside?(point, city_map)
+  x, y = point
+  height = city_map.length
+  width = city_map[0].length
+  x.between?(0, height - 1) && y.between?(0, width - 1)
+end
+
+def count_antenna(city_map)
+  counter = Hash.new { |h, k| h[k] = [] }
+  antenna = Set.new
+
+  city_map.each_with_index do |line, i|
+    line.each_with_index do |cell, j|
+      next if cell == '.'
+      antenna.add([i, j])
+      counter[cell] << [i, j]
+    end
+  end
+
+  [counter, antenna]
+end
+
+def solution(input)
+  city_map = input.split("\n").map(&:chars)
+  counter, antinodes = count_antenna(city_map)
+
+  counter.each_value do |positions|
+    positions.combination(2).each do |p1, p2|
+      dx, dy = p1[0] - p2[0], p1[1] - p2[1]
+
+      [[p1, [dx, dy]], [p2, [-dx, -dy]]].each do |start, delta|
+        current = [start[0] + delta[0], start[1] + delta[1]]
+        while inside?(current, city_map)
+          antinodes.add(current)
+          current = [current[0] + delta[0], current[1] + delta[1]]
+        end
+      end
+    end
+  end
+
+  print_city_map(city_map, antinodes)
+  antinodes.size
+end

2024/day8/sample.txt

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+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............