Added Stack (#14)

* Array implementation of stacks have been added.
* `misc_util` has been added to avoid repeated code.

Author: czgdp1807

.gitignore

@@ -4,3 +4,4 @@ __pycache__/
 *.pyo
 .vscode/
 .pytest_cache/
+pre_commit.ps1

.travis.yml

@@ -5,4 +5,5 @@ python:
 install:
         - pip install -r requirements.txt
 script:
+        - python -m unittest discover pydatastructs
         - pytest --doctest-modules

AUTHORS

@@ -1 +1,3 @@
 Gagandeep Singh<singh.23@iitj.ac.in>
+Kartikei Mittal<kartikeimittal@gmail.com>
+

pydatastructs/__init__.py

@@ -1,2 +1,4 @@
 from .linear_data_structures import *
 from .trees import *
+from .miscellaneous_data_structures import *
+from .utils import *

pydatastructs/linear_data_structures/__init__.py

@@ -1,6 +1,9 @@
 __all__ = []
 
-from . import arrays
+from . import (
+    arrays,
+)
+
 from .arrays import (
     OneDimensionalArray,
 )

pydatastructs/linear_data_structures/arrays.py

@@ -1,12 +1,10 @@
 from __future__ import print_function, division
+from pydatastructs.utils.misc_util import _check_type, NoneType
 
 __all__ = [
 'OneDimensionalArray'
 ]
 
-_check_type = lambda a, t: isinstance(a, t)
-NoneType = type(None)
-
 class Array(object):
     '''
     Abstract class for arrays in pydatastructs.
@@ -105,7 +103,10 @@ def __getitem__(self, i):
         return self._data.__getitem__(i)
 
     def __setitem__(self, idx, elem):
-        self._data[idx] = self._dtype(elem)
+        if elem is None:
+            self._data[idx] = None
+        else:
+            self._data[idx] = self._dtype(elem)
 
     def fill(self, elem):
         elem = self._dtype(elem)

pydatastructs/miscellaneous_data_structures/__init__.py

@@ -0,0 +1,10 @@
+__all__ = []
+
+from . import (
+    stack,
+)
+
+from .stack import (
+    Stack,
+)
+__all__.extend(stack.__all__)

pydatastructs/miscellaneous_data_structures/stack.py

@@ -0,0 +1,114 @@
+
+from __future__ import print_function, division
+from pydatastructs.linear_data_structures import OneDimensionalArray
+from copy import deepcopy as dc
+
+__all__ = [
+    'Stack'
+]
+
+_check_type = lambda a, t: isinstance(a, t)
+NoneType = type(None)
+
+class Stack(object):
+    """Respresentation of stack data structure
+
+    Parameters
+    ==========
+
+    implementation : str
+        Implementation to be used for stack.
+        By default, 'array'
+        Currently only supports 'array'
+        implementation.
+    maxsize : int
+        The maximum size of the stack.
+        For array implementation.
+    top : int
+        The top element of the stack.
+        For array implementation.
+    items : OneDimensionalArray
+        Optional, by default, None
+        The inital items in the stack.
+        For array implementation.
+    dtype : A valid python type
+        Optional, by default int if item
+        is None, otherwise takes the data
+        type of OneDimensionalArray
+        For array implementation.
+
+    Example
+    =======
+
+    >>> from pydatastructs import Stack
+    >>> s = Stack(maxsize=5, top=0)
+    >>> s.push(1)
+    >>> s.push(2)
+    >>> s.push(3)
+    >>> str(s)
+    '[1, 2, 3, None, None]'
+    >>> 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('maxsize', None),
+                kwargs.get('top', None),
+                kwargs.get('items', None),
+                kwargs.get('dtype', int))
+        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.")
+
+class ArrayStack(Stack):
+
+    def __new__(cls, maxsize=None, top=0, items=None, dtype=int):
+        if not _check_type(maxsize, int):
+            raise ValueError("maxsize is missing.")
+        if not _check_type(top, int):
+            raise ValueError("top is missing.")
+        if items == None:
+            items = OneDimensionalArray(dtype, maxsize)
+        if not _check_type(items, OneDimensionalArray):
+            raise ValueError("items is not of type, OneDimensionalArray")
+        if items._size > maxsize:
+            raise ValueError("Overflow, size of items %s is greater "
+                            "than maxsize, %s"%(items._size, maxsize))
+        obj = object.__new__(cls)
+        obj.maxsize, obj.top, obj.items, obj.dtype = \
+            maxsize, top, items, items._dtype
+        return obj
+
+    def push(self, x):
+        if self.top == self.maxsize:
+            raise ValueError("Stack is full.")
+        self.items[self.top] = self.dtype(x)
+        self.top += 1
+
+    def pop(self):
+        if self.top == 0:
+            raise ValueError("Stack is already empty.")
+        self.top -= 1
+        r = self.items[self.top]
+        self.items[self.top] = None
+        return r
+
+    def __str__(self):
+        """
+        Used for printing.
+        """
+        return str(self.items._data)

pydatastructs/miscellaneous_data_structures/tests/__init__.py

@@ -0,0 +1,22 @@
+from pydatastructs.miscellaneous_data_structures import Stack
+from pydatastructs.linear_data_structures import OneDimensionalArray
+from pydatastructs.utils.raises_util import raises
+
+def test_Stack():
+
+    s = Stack(maxsize=3, top=0)
+    s.push(1)
+    s.push(2)
+    s.push(3)
+    assert s.top == 3
+    assert str(s) == '[1, 2, 3]'
+    raises(ValueError, lambda: s.push(4))
+    assert s.pop() == 3
+    assert s.pop() == 2
+    assert s.pop() == 1
+    assert s.top == 0
+    raises(ValueError, lambda: s.pop())
+    raises(ValueError, lambda: Stack())
+    raises(ValueError, lambda: Stack(maxsize=5, top=0, items=[1, 2, 3]))
+    raises(ValueError, lambda: Stack(maxsize=5, top=0,
+                        items=OneDimensionalArray(6)))