Day ten

10.input

@@ -0,0 +1,40 @@
+1237651012319765432345545498010145891010
+0348943105408894001056654584321036712329
+9432342236717433145677723675490121903478
+8541051549826522238988812106789030876569
+7650760678434011032349900125699845686788
+6789898730569545601456987234016768798697
+4372123621078438780767076543223609894556
+5201014532321029892898123456104510983045
+6102306545452310121234010767040125672130
+7985430696101402100765109898234534343421
+8976521787210569011843210982129653254321
+8907823474389678123954301011018762169870
+7010910567478012335869832109800121078765
+6327823498565723546778789236789630989034
+5436910989367874695219654345676547876123
+6785403873456965784301105654565670945210
+5690342762106543287012234787654981234678
+4301201659014690196543989898943272221589
+5210112348323787017432170101032102100450
+1290010167654896528903061232589043678321
+0381201233210743434012354345672154509100
+5470300344984652143023403456983893210234
+6565415455675430032110512987870765210985
+7432326966556721243329601070121894387876
+8901457877876898358478732112434721296901
+9450962340945876569569540003965780105432
+2365871651232903478757651654875698987321
+1671010787891212349808932787034567076670
+0982107896500301256710149890123498125583
+1210212783410450901223456781210321034492
+0398347894323467814345069890323498503301
+3457656321301556030196178765432567412212
+6569845490219698123287234076781064565801
+7078780185428787654876543189899873278921
+8129698276538988140989812278734765103210
+9234567345445679031256701345625654014765
+0103216548765678120349810566010103425894
+0987607239854581234569809870987912436723
+1234568120123290107678712561296876543010
+2109879011234103238932103450345689832123

10.rb

@@ -0,0 +1,72 @@
+#!/usr/bin/env ruby
+
+require "debug"
+
+problem = 10
+@input = File.readlines("#{problem}.input")
+#@input = DATA.read.split("\n")
+  .map { _1.strip.chars.map { |c| c == "." ? "." : c.to_i }}
+@debug = @input.size < 20
+#@debug = true
+
+def bounded?(point)
+  point.first >= 0 &&
+    point.last >= 0 &&
+    point.first < @input.size &&
+    point.last < @input.first.size
+end
+
+def traverse(start, height = 1)
+  result = [
+    [start.first - 1, start.last],
+    [start.first + 1, start.last],
+    [start.first, start.last - 1],
+    [start.first, start.last + 1]
+  ].map do |point|
+    if !bounded?(point) || @input.dig(*point) == "."
+      []
+    elsif @input.dig(*point) == 9 && height == 9
+      if @debug
+        @paths[point.first][point.last] = @input.dig(*point)
+      end
+      [point]
+    elsif @input.dig(*point) == height
+      traverse(point, height + 1).flatten(1)
+    else # if @input.dig(*point) != height
+      []
+    end
+  end
+
+  if result.size > 0 && @debug
+    @paths[start.first][start.last] = @input.dig(*start)
+  end
+
+  result
+end
+
+if @debug
+  @paths = Array.new(@input.size) { Array.new(@input.first.size) { "." } }
+end
+
+result = (0...@input.size).flat_map do |x|
+  (0...@input.first.size).map do |y|
+    [[x, y], traverse([x, y]).flatten(1)] if @input[x][y] == 0
+  end.compact
+end.to_h
+
+if @debug
+  puts @paths.map(&:join).join("\n")
+end
+
+p result.values.map { _1.uniq.size }.sum
+p result.values.map { _1.size }.sum
+
+__END__
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732