[WIP] Added Stacks Using Linked List

.gitignore

@@ -48,6 +48,8 @@ htmlcov
 *~
 __pycache__/
 .pytest_cache/
+build/
+dist/
 
 # Backup Files #
 ################

CODE_OF_CONDUCT.md

@@ -12,7 +12,7 @@ appearance, race, religion, or sexual identity and orientation.
 ## Our Standards
 
 Examples of behavior that contributes to creating a positive environment
-include:
+
 
 * Using welcoming and inclusive language
 * Being respectful of differing viewpoints and experiences

build/lib/pydatastructs/miscellaneous_data_structures/linked_stacks.py

@@ -0,0 +1,25 @@
+from pydatastructs import SinglyLinkedList
+
+__all__ = ["Linked_Stacks"]
+class Linked_Stacks:
+
+    # A class to implement Stacks Built over Singly Linked Lists
+
+    def __init__(self):
+        self.sll = SinglyLinkedList()
+        self.top = self.sll.head
+
+    def push(self,data):
+        self.sll.append(data)
+        if self.top is None:
+            self.top = self.sll.head
+        return self
+
+    def pop(self):
+        if self.top is not None:
+            self.data = self.top.data
+            self.top = self.top.next
+        return self.data
+
+    def peek(self):
+        return self.top.data

build/lib/pydatastructs/miscellaneous_data_structures/stack.py

@@ -0,0 +1,184 @@
+from pydatastructs.linear_data_structures import DynamicOneDimensionalArray
+from pydatastructs.utils.misc_util import _check_type, NoneType
+from copy import deepcopy as dc
+from pydatastructs import SinglyLinkedList
+from pydatastructs import DoublyLinkedList
+
+__all__ = [
+    'Stack'
+]
+
+class Stack(object):
+    """Representation of stack data structure
+
+    Parameters
+    ==========
+
+    implementation : str
+        Implementation to be used for stack.
+        By default, 'array'
+        Currently only supports 'array'
+        implementation.
+    items : list/tuple
+        Optional, by default, None
+        The inital items in the stack.
+        For array implementation.
+    dtype : A valid python type
+        Optional, by default NoneType if item
+        is None, otherwise takes the data
+        type of DynamicOneDimensionalArray
+        For array implementation.
+
+    Examples
+    ========
+
+    >>> from pydatastructs import Stack
+    >>> s = Stack()
+    >>> s.push(1)
+    >>> s.push(2)
+    >>> s.push(3)
+    >>> str(s)
+    '[1, 2, 3]'
+    >>> s.pop()
+    3
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Stack_(abstract_data_type)
+    """
+
+    def __new__(cls, implementation='array', **kwargs):
+        if implementation == 'array':
+            return ArrayStack(
+                kwargs.get('items', None),
+                kwargs.get('dtype', int))
+
+        elif implementation == "ll":
+            return Linked_Stacks()
+
+        raise NotImplementedError(
+                "%s hasn't been implemented yet."%(implementation))
+
+
+    def push(self, *args, **kwargs):
+        raise NotImplementedError(
+            "This is an abstract method.")
+
+    def pop(self, *args, **kwargs):
+        raise NotImplementedError(
+              "This is an abstract method.")
+
+    @property
+    def is_empty(self):
+        return None
+
+    @property
+    def peek(self):
+        return None
+
+class ArrayStack(Stack):
+
+    __slots__ = ['items']
+
+    def __new__(cls, items=None, dtype=NoneType):
+        if items is None:
+            items = DynamicOneDimensionalArray(dtype, 0)
+        else:
+            items = DynamicOneDimensionalArray(dtype, items)
+        obj = object.__new__(cls)
+        obj.items = items
+        return obj
+
+    def push(self, x):
+        if self.is_empty:
+            self.items._dtype = type(x)
+        self.items.append(x)
+
+    def pop(self):
+        if self.is_empty:
+            raise ValueError("Stack is empty")
+
+        top_element = dc(self.items[self.items._last_pos_filled])
+        self.items.delete(self.items._last_pos_filled)
+        return top_element
+
+    @property
+    def is_empty(self):
+        return self.items._last_pos_filled == -1
+
+    @property
+    def peek(self):
+        return self.items[self.items._last_pos_filled]
+
+    def __str__(self):
+        """
+        Used for printing.
+        """
+        return str(self.items._data)
+
+class Linked_Stacks(Stack):
+
+    """Representation of Stack Data Structure using Doubly Linked List
+    Methods
+    ===========
+    push : 
+    A normal push operation to the Stack
+    
+    pop : 
+    Delete the top most element from the stack
+    Returns the value of top element
+
+    peek :
+    returns the value of top element
+
+    is_empty :
+    Checks for whether a Stack is been empty or not
+    Return True if empty else False
+
+    __str__ : 
+    Used for Printing the Stack
+
+    """
+    __slots__ = ["dll"]
+    def __new__(cls):
+        dll = DoublyLinkedList() 
+        obj = object.__new__(cls)
+        obj.dll = dll
+        obj.top = dll.head
+        return obj
+
+
+    def push(self,data):
+        self.dll.append(data)
+        if self.top is None:
+            self.top = self.dll.head
+        self.top = self.top.next
+
+    def pop(self):
+        if not self.is_empty:
+            self.data = self.top.data
+            self.top = self.top.prev
+            return self.data
+        else:
+            return "Stack is empty"
+
+
+    @property
+    def is_empty(self):
+        if self.top == None:
+            return 1
+        return 0
+
+    @property
+    def peek(self):
+        if self.top is not None:
+            return self.top.data
+        return "Stack is empty"
+
+    def __str__(self):
+        "Used for Printing the Stack"
+        iterator = self.top
+        while iterator is not None:
+            print(iterator.data)
+            iterator = iterator.next

pydatastructs/miscellaneous_data_structures/stack.py

@@ -1,6 +1,7 @@
 from pydatastructs.linear_data_structures import DynamicOneDimensionalArray
 from pydatastructs.utils.misc_util import _check_type, NoneType
 from copy import deepcopy as dc
+from pydatastructs import DoublyLinkedList
 
 __all__ = [
     'Stack'
@@ -51,9 +52,14 @@ def __new__(cls, implementation='array', **kwargs):
             return ArrayStack(
                 kwargs.get('items', None),
                 kwargs.get('dtype', int))
+
+        elif implementation == "ll":
+            return Linked_Stacks()
+
         raise NotImplementedError(
                 "%s hasn't been implemented yet."%(implementation))
 
+
     def push(self, *args, **kwargs):
         raise NotImplementedError(
             "This is an abstract method.")
@@ -109,3 +115,68 @@ def __str__(self):
         Used for printing.
         """
         return str(self.items._data)
+
+class Linked_Stacks(Stack):
+
+    """Representation of Stack Data Structure using Doubly Linked List
+    Methods
+    ===========
+    push :
+    A normal push operation to the Stack
+
+    pop :
+    Delete the top most element from the stack
+    Returns the value of top element
+
+    peek :
+    returns the value of top element
+
+    is_empty :
+    Checks for whether a Stack is been empty or not
+    Return True if empty else False
+
+    __str__ :
+    Used for Printing the Stack
+
+    """
+    __slots__ = ["dll"]
+    def __new__(cls):
+        dll = DoublyLinkedList()
+        obj = object.__new__(cls)
+        obj.dll = dll
+        obj.top = dll.head
+        return obj
+
+
+    def push(self,data):
+        self.dll.append(data)
+        if self.top is None:
+            self.top = self.dll.head
+        self.top = self.top.next
+
+    def pop(self):
+        if not self.is_empty:
+            self.data = self.top.data
+            self.top = self.top.prev
+            return self.data
+        else:
+            return "Stack is empty"
+
+    @property
+    def is_empty(self):
+        if self.top is None:
+            return 1
+        return 0
+
+    @property
+    def peek(self):
+        if self.top is not None:
+            return self.top.data
+        return "Stack is empty"
+
+    def __str__(self):
+        "Used for Printing the Stack"
+        iterator = self.top
+        while iterator is not None:
+            print(iterator.data)
+            iterator = iterator.next