1 files changed, 233 insertions, 0 deletions
diff --git a/20/b-combine.lua b/20/b-combine.lua
new file mode 100644
index 0000000..f5d176c
--- /dev/null
+++ b/20/b-combine.lua
@@ -0,0 +1,233 @@
+Tile = {}
+Tile.__index = Tile
+
+Tile.__tostring = function(self)
+    string = ''
+    for i = 1, 10 do
+        for j = 1, 10 do
+            string = string .. self:get(i, j) .. ' '
+        end
+        string = string .. "\n"
+    end
+
+    return string
+end
+
+function id(x, y)
+    return x, y
+end
+
+function Tile:new(tile)
+    local object = {}
+    object.tile = tile
+    object.transform = id
+    return setmetatable(object, self)
+end
+
+function Tile:rotate()
+    local old_transform = self.transform
+    self.transform = function(x, y)
+        return old_transform(y, 10 - x + 1)
+    end
+end
+
+function Tile:flip()
+    local old_transform = self.transform
+    self.transform = function(x, y)
+        return old_transform(x, 10 - y + 1)
+    end
+end
+
+function Tile:get(x, y)
+    x, y = self.transform(x, y)
+    return self.tile[x][y]
+end
+
+function Tile:border(horizontal, index)
+    first_column = 0
+    first_row = 0
+    last_column = 0
+    last_row = 0
+    if horizontal then
+        first_column = 1
+        last_column = 10
+        first_row = index
+        last_row = index
+    else
+        first_column = index
+        last_column = index
+        first_row = 1
+        last_row = 10
+    end
+
+    b = ''
+    for row = first_row, last_row do
+        for column = first_column, last_column do
+            b = b .. self:get(row, column)
+        end
+    end
+
+    if (horizontal and index > 1) or (not horizontal and index == 1) then
+        b = b:reverse()
+    end
+
+    return b
+end
+
+function Tile:borders()
+    return {
+        self:border(true, 1),
+        self:border(true, 10),
+        self:border(false, 1),
+        self:border(false, 10)
+    }
+end
+
+Board = {}
+Board.__index = Board
+
+function Board:new(corner)
+    object = {}
+    object.board = {}
+    object.board[1] = {}
+    object.board[1][1] = corner
+    return setmetatable(object, self)
+end
+
+function Board:try_add(x, y, tile)
+    if not self.board[x] then self.board[x] = {} end
+    local reference_tile = self.board[x][y - 1]
+    below = false
+    if not reference_tile then
+        below = true
+        reference_tile = self.board[x - 1][y]
+    end
+
+    assert(reference_tile, "tried to insert tile at non-connected location")
+
+    orientation_matches = function() return false end
+    if below then
+        orientation_matches = function()
+            return reference_tile:border(true, 10) == tile:border(true, 1):reverse()
+        end
+    else
+        orientation_matches = function()
+            return reference_tile:border(false, 10) == tile:border(false, 1):reverse()
+        end
+    end
+
+    correctly_rotated = false
+    for i = 1, 4 do
+        if orientation_matches() then
+            correctly_rotated = true
+            break
+        end
+        tile:rotate()
+    end
+
+    if not correctly_rotated then
+        tile:flip()
+        for i = 1, 4 do
+            if orientation_matches() then
+                correctly_rotated = true
+                break
+            end
+            tile:rotate()
+        end
+    end
+
+    if correctly_rotated then
+        if not self.board[x] then
+            self.board[x] = {}
+        end
+        self.board[x][y] = tile
+    end
+      
+    return correctly_rotated
+end
+
+tiles = {}
+current_tile_number = nil
+current_tile = {}
+
+for line in io.lines('input.txt') do
+    if line == "" and current_tile_number then
+        tiles[current_tile_number] = Tile:new(current_tile)
+        current_tile = {}
+    end
+
+    space_index = line:find(' ')
+
+    if space_index then
+        current_tile_number = line:sub(space_index+1, -2)
+    elseif #line > 0 then
+        row = {}
+        for i = 1, line:len() do
+            table.insert(row, line:sub(i, i))
+        end
+        table.insert(current_tile, row)
+    end
+end
+
+corner = '1327'
+corner_tile = tiles[corner]
+corner_tile:flip()
+
+board = Board:new(tiles[corner])
+
+handled = {}
+handled[corner] = true
+
+visited = {}
+visited[1] = {}
+visited[1][1] = true
+visited[2] = {}
+visited[2][1] = true
+visited[1][2] = true
+
+queue = {}
+table.insert(queue, {1, 2})
+table.insert(queue, {2, 1})
+while #queue ~= 0 do
+    current = table.remove(queue, 1)
+    x = current[1]
+    y = current[2]
+    inserted = false
+    for tile_id, tile in pairs(tiles) do
+        if not handled[tile_id] then
+            if board:try_add(x, y, tile) then
+                assert(board.board[x][y])
+                inserted = true
+                handled[tile_id] = true
+
+                if not visited[x] then visited[x] = {} end
+                if not visited[x + 1] then visited[x + 1] = {} end
+                if x < 12 and not visited[x + 1][y] then
+                    table.insert(queue, {x + 1, y})
+                    visited[x + 1][y] = true
+                end
+                if y < 12 and not visited[x][y + 1] then
+                    table.insert(queue, {x, y + 1})
+                    visited[x][y + 1] = true
+                end
+                break
+            end
+        end
+    end
+    if not inserted then
+        print('failed')
+        break
+    end
+end
+
+for i = 1, 12 do
+    for x = 2, 9 do
+        for j = 1, 12 do
+            local tile = board.board[i][j]
+            for y = 2, 9 do
+                io.write(tile:get(x, y))
+            end
+        end
+        print()
+    end
+end