Create design-front-middle-back-queue.py

Author: kamyu104

Python/design-front-middle-back-queue.py

@@ -0,0 +1,65 @@
+# Time:  O(1)
+# Space: O(n)
+
+import collections
+
+
+class FrontMiddleBackQueue(object):
+
+    def __init__(self):
+        self.__left, self.__right = collections.deque(), collections.deque()   
+
+    def pushFront(self, val):
+        """
+        :type val: int
+        :rtype: None
+        """
+        self.__left.appendleft(val)
+        self.__balance()        
+
+    def pushMiddle(self, val):
+        """
+        :type val: int
+        :rtype: None
+        """
+        if len(self.__left) > len(self.__right):
+            self.__right.appendleft(self.__left.pop())
+        self.__left.append(val)
+
+    def pushBack(self, val):
+        """
+        :type val: int
+        :rtype: None
+        """
+        self.__right.append(val)
+        self.__balance()
+
+    def popFront(self):
+        """
+        :rtype: int
+        """
+        val = (self.__left or collections.deque([-1])).popleft()
+        self.__balance()
+        return val
+
+    def popMiddle(self):
+        """
+        :rtype: int
+        """
+        val = (self.__left or [-1]).pop()
+        self.__balance()
+        return val
+
+    def popBack(self):
+        """
+        :rtype: int
+        """
+        val = (self.__right or self.__left or [-1]).pop()
+        self.__balance()
+        return val
+
+    def __balance(self):
+        if len(self.__left) > len(self.__right)+1:
+            self.__right.appendleft(self.__left.pop())
+        elif len(self.__left) < len(self.__right):
+            self.__left.append(self.__right.popleft())