Added Queue data structure

pydatastructs/miscellaneous_data_structures/__init__.py

@@ -14,3 +14,8 @@
     Stack,
 )
 __all__.extend(stack.__all__)
+
+from .queue import (
+    Queue,
+)
+__all__.extend(queue.__all__)

pydatastructs/miscellaneous_data_structures/queue.py

@@ -0,0 +1,95 @@
+from pydatastructs.linear_data_structures import DynamicOneDimensionalArray
+
+__all__ = [
+    'Queue'
+]
+
+class Queue(object):
+    """Representation of queue data structure
+
+    Examples
+    ========
+
+    >>> from pydatastructs import Queue
+    >>> q = Queue()
+    >>> q.append(1)
+    >>> q.append(2)
+    >>> q.append(3)
+    >>> q.popleft()
+    >>> q.len()
+    1
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Queue_(abstract_data_type)
+    """
+
+    def __new__(cls, implementation='array', **kwargs):
+        if implementation == 'array':
+            return ArrayQueue(
+                kwargs.get('items', None),
+                kwargs.get('dtype', int))
+        raise NotImplementedError(
+                "%s hasn't been implemented yet."%(implementation))
+
+    def append(self, *args, **kwargs):
+        raise NotImplementedError(
+            "This is an abstract method.")
+
+    def popleft(self, *args, **kwargs):
+        raise NotImplementedError(
+            "This is an abstract method.")
+
+    @property
+    def is_empty(self):
+        return self.front == -1
+
+    @property
+    def is_full(self):
+        return ((self.rear + 1) % self.size == self.front)
+
+class ArrayQueue(Queue):
+
+    __slots__ = ['items', 'dtype']
+
+    def __new__(cls, items=None, dtype=int):
+        if items is None:
+            items = DynamicOneDimensionalArray(dtype, 0)
+        else:
+            items = DynamicOneDimensionalArray(dtype, items)
+        obj = object.__new__(cls)
+        obj.items, obj.dtype = \
+            items, items._dtype
+        return obj
+
+    def __init__(self):
+        self.items.size = size
+        self.items = [None for i in range(size)]
+        self.items.front = self.items.rear = -1
+
+    def append(self, x):
+        if self.is_full:
+            raise ValueError("Queue is full")
+        elif (self.items.front == -1):
+            self.items.front = 0
+            self.items.rear = 0
+            self.items[self.items.rear] = x
+        else:
+            self.items.rear = (self.items.rear + 1) % self.size
+            self.items[self.items.rear] = x
+
+    def popleft(self):
+        if self.is_empty:
+            raise ValueError("Queue is empty")
+        elif (self.items.front == self.items.rear):
+            self.items.front = -1
+            self.items.rear = -1
+            return self.items[self.items.front]
+        else:
+            self.items.front = (self.items.front + 1) % self.size
+            return self.items[self.items.front]
+
+    def len(self):
+        return abs(abs(self.size - self.items.front) - abs(self.size - self.items.rear))+1
+

pydatastructs/miscellaneous_data_structures/stack.py

@@ -9,7 +9,7 @@
 NoneType = type(None)
 
 class Stack(object):
-    """Respresentation of stack data structure
+    """Representation of stack data structure
 
     Parameters
     ==========
@@ -29,8 +29,8 @@ class Stack(object):
         type of OneDimensionalArray
         For array implementation.
 
-    Example
-    =======
+    Examples
+    ========
 
     >>> from pydatastructs import Stack
     >>> s = Stack()

pydatastructs/miscellaneous_data_structures/tests/test_queue.py

@@ -0,0 +1,12 @@
+from pydatastructs.miscellaneous_data_structures import Queue
+from pydatastructs.utils.raises_util import raises
+
+def test_Queue():
+
+    q = Queue()
+    q.append(1)
+    q.append(2)
+    q.append(3)
+    assert q.popleft() == 1
+    assert q.popleft() == 2
+    assert q.len() == 1