[Update] 优化树结构

apps/common/struct.py

@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+#
+
+
+class Stack(list):
+    def is_empty(self):
+        return len(self) == 0
+
+    @property
+    def top(self):
+        if self.is_empty():
+            return None
+        return self[-1]
+
+    @property
+    def bottom(self):
+        if self.is_empty():
+            return None
+        return self[0]
+
+    def size(self):
+        return len(self)
+
+    def push(self, item):
+        self.append(item)