Add day 12 part 1 solution

day12.cr

@@ -0,0 +1,75 @@
+require "advent"
+INPUT = input(2022, 12).lines.map(&.chars) 
+EDGES = {} of Tuple(Int32,Int32) => Array(Tuple(Int32, Int32))
+
+def add_at(pos, c, x, y)
+  return unless y >= 0 && y < INPUT.size
+  return unless x >= 0 && x < INPUT[0].size
+
+  o = INPUT[y][x]
+  o = 'a' if o == 'S'
+  o = 'z' if o == 'E'
+
+  return if (o.ord-c.ord) > 1
+  EDGES[pos] << ({x,y});
+end
+
+def add_nearby(x, y)
+  c = INPUT[y][x]
+  c = 'a' if c == 'S'
+  c = 'z' if c == 'E'
+
+  if !EDGES[{x,y}]?
+    EDGES[{x,y}] = [] of Tuple(Int32,Int32)
+  end
+  add_at({x,y}, c, x+1, y)
+  add_at({x,y}, c, x-1, y)
+  add_at({x,y}, c, x, y+1)
+  add_at({x,y}, c, x, y-1)
+end
+
+from = {0,0}
+to = {0,0}
+INPUT.each_with_index do |row, y|
+  row.each_with_index do |c, x|
+    pos = {x, y}
+    add_nearby(x, y)
+    from = pos if c == 'S'
+    to = pos if c == 'E'
+  end
+end
+
+costs = {from => 0}
+visited = Set(Tuple(Int32, Int32)).new
+
+while !costs.empty?
+  k, v = costs.min_by do |k,v|
+    v
+  end
+
+  if k == to
+    puts "Found! #{v}"
+    break
+  end
+
+  costs.delete k
+  visited << k
+  INPUT[k[1]][k[0]] = INPUT[k[1]][k[0]].upcase
+  puts k
+
+  EDGES[k].each do |edge|
+    next if visited.includes? edge
+    if old = costs[edge]?
+      costs[edge] = v+1 if old > v+1
+    else
+      costs[edge] = v+1
+    end
+  end
+end
+
+INPUT.each do |line|
+  line.each do |c|
+    print c
+  end
+  puts
+end