add Map._finalize()

Map.py

@@ -3,15 +3,19 @@
 class Map(object):
     def __init__(self):
         self._arr = []
+        self._list = []
+        self._finalized = False
 
     def add(self, row, col, tile):
         self._extend(row, col)
         self._arr[row][col] = tile
+        self._list.append(tile)
+        self._finalized = False
 
     def get(self, row, col):
-        if len(self._arr) <= row:
+        if row < 0 or len(self._arr) <= row:
             return None
-        if len(self._arr[row]) <= col:
+        if col < 0 or len(self._arr[row]) <= col:
             return None
         return self._arr[row][col]
 
@@ -20,3 +24,27 @@ class Map(object):
             self._arr.append([])
         while len(self._arr[row]) <= col:
             self._arr[row].append(None)
+
+    def _finalize(self):
+        if self._finalized:
+            return
+        self._neighbors = {}
+        def check(_r, _c, tile):
+            n = self.get(_r, _c)
+            if n:
+                self._neighbors[_c].append(n)
+        for row, r in enumerate(self._arr):
+            for col, tile in enumerate(r):
+                if tile:
+                    self._neighbors[tile] = []
+                    offset = row & 1
+                for i in range(2):
+                    c = col - 1 + i + offset
+                    check(row - 1, c)
+                    check(row + 1, c)
+                check(row, col - 1)
+                check(row, col + 1)
+        self._finalized = True
+
+    def number(self):
+        self._finalize()