Year 2024 Day 10

2024/day10.rb

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+map = STDIN.read.split("\n").map { |line| line.chars.map(&:to_i) }
+
+DELTAS = [
+  [-1, 0],
+  [1, 0],
+  [0, -1],
+  [0, 1]
+]
+
+def bfs_score(map, start_i, start_j)
+  queue = [[start_i, start_j, 0]]
+  peaks = Set.new
+  p2_score = 0
+  while !queue.empty?
+    i, j, height = queue.shift
+    DELTAS.each do |di, dj|
+      ni, nj = i + di, j + dj
+      next if ni < 0 || ni >= map.size || nj < 0 || nj >= map.first.size
+
+      neighbor = map[ni][nj]
+      next unless height + 1 == neighbor
+
+      if neighbor == 9
+        peaks << [ni, nj]
+        p2_score += 1
+      else
+        queue << [ni, nj, neighbor]
+      end
+    end
+  end
+  [peaks.size, p2_score]
+end
+
+trail_heads = []
+0.upto(map.size - 1).each do |i|
+  0.upto(map.first.size - 1).each do |j|
+    trail_heads << [i, j] if map[i][j] == 0
+  end
+end
+
+puts trail_heads.map { |(i, j)| bfs_score(map, i, j) }.reduce { |(p1, p2), (s1, s2)| [p1 + s1, p2 + s2] }

2024/examples/day10.txt

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+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732