1 files changed, 108 insertions, 0 deletions
diff --git a/20/b-find.lua b/20/b-find.lua
new file mode 100644
index 0000000..800fc6e
--- /dev/null
+++ b/20/b-find.lua
@@ -0,0 +1,108 @@
+function parse_row(line)
+    row = {}
+    for i = 1, #line do
+        table.insert(row, line:sub(i, i))
+    end
+    return row
+end
+Map = {}
+Map.__index = Map
+
+Map.__tostring = function(self)
+    string = ''
+    for i = 1, 96 do
+        for j = 1, 96 do
+            string = string .. self:get(i, j) .. ' '
+        end
+        string = string .. "\n"
+    end
+
+    return string
+end
+
+function Map:get(x, y)
+    x, y = self.transform(x, y)
+    return self.map[x][y]
+end
+
+function id(x, y)
+    return x, y
+end
+
+function Map:new(map)
+    local object = {}
+    object.map = map
+    object.transform = id
+    return setmetatable(object, self)
+end
+
+function Map:rotate()
+    local old_transform = self.transform
+    self.transform = function(x, y)
+        return old_transform(y, 96 - x + 1)
+    end
+end
+
+function Map:flip()
+    local old_transform = self.transform
+    self.transform = function(x, y)
+        return old_transform(x, 96 - y + 1)
+    end
+end
+
+function Map:has_monster(x, y)
+    if x + #monster > 96 then
+        print('x too large')
+        return false
+    end
+    if y + #monster[1] > 96 then
+        print('y too large')
+        return false
+    end
+    for i = 1, #monster do
+        for j = 1, #monster[1] do
+            if monster[i][j] == '#' and self:get(x+i, y+j) ~= '#' then
+                return false
+            end
+        end
+    end
+
+    return true
+end
+
+monster = {}
+monster[1] = parse_row('                  # ')
+monster[2] = parse_row('#    ##    ##    ###')
+monster[3] = parse_row(' #  #  #  #  #  #   ')
+
+map = {}
+for line in io.lines('combined') do
+    table.insert(map, parse_row(line))
+end
+
+map = Map:new(map)
+map:flip()
+map:rotate()
+map:rotate()
+map:rotate()
+
+count = 0
+for x = 1, 96 - #monster do
+    for y = 1, 96 - #monster[1] do
+        if map:has_monster(x, y) then
+            count = count + 1
+        end
+    end
+end
+
+hashes = 0
+for i = 1, 96 do
+    for j = 1, 96 do
+        if map.map[i][j] == '#' then
+            hashes = hashes + 1
+        end
+    end
+end
+
+result = hashes - count * 15
+print(result)