Module grscheller.datastructures.stack
Expand source code
# Copyright 2023 Geoffrey R. Scheller
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from __future__ import annotations
"""LIFO stack:
Module implementing a LIFO stack using a singularly linked linear tree of nodes.
The nodes can be safely shared between different Stack instances. Pushing to,
popping from, and getting the length of the stack are all O(1) operations.
"""
__all__ = ['Stack']
__author__ = "Geoffrey R. Scheller"
__copyright__ = "Copyright (c) 2023 Geoffrey R. Scheller"
__license__ = "Appache License 2.0"
from .functional import Maybe, Some, Nothing
class _Node:
"""Class implementing nodes that can be linked together to form a singularly
linked list. A node always contain data. It either has a reference to the
next _Node object or None to indicate the bottom of the linked list.
"""
def __init__(self, data, nodeNext: _Node | None):
self._data = data
self._next = nodeNext
def __bool__(self):
return True
class Stack():
"""Class implementing a Last In, First Out (LIFO) stack datastructure. The
stack contains a singularly linked list of nodes.
- The stack points to either the top node in the list, or to None to
indicate an empty stack.
- Stacks are stateful objects where values can be pushed on & popped off.
- None represents the absence of a value and are ignored if pushed on the
stack.
"""
def __init__(self, *data):
"""
Parameters
----------
*data : 'any'
Any data to prepopulate the stack.
The data is pushed onto the stack left to right.
None values are ignored and not pushed on stack.
"""
self._head = None
self._count = 0
for datum in data:
if datum is not None:
node = _Node(datum, self._head)
self._head = node
self._count += 1
def __len__(self):
"""Returns current number of values on the stack"""
return self._count
def isEmpty(self) -> bool:
"""Test if stack is empty"""
return self._count == 0
def __iter__(self):
"""Iterator yielding data stored in the stack, does not consume data."""
node = self._head
while node:
yield node._data
node = node._next
def __eq__(self, other):
"""
Returns True if all the data stored on the two stacks are the same.
Worst case is O(n) behavior which happens when all the corresponding
data elements on the two stacks are equal, in whatever sense they
define equality, and none of the nodes are shared.
Parameters
----------
other : 'any'
"""
if not isinstance(other, type(self)):
return False
if self._count != other._count:
return False
left = self
right = other
nn = self._count
while nn > 0:
if left is None or right is None:
return True
if left._head is right._head:
return True
if left.head() != right.head():
return False
left = left.tail().getOrElse(Stack())
right = right.tail().getOrElse(Stack())
nn -= 1
return True
def __repr__(self):
"""Display the data in the stack."""
dataListStrs = []
for data in self:
dataListStrs.append(repr(data))
dataListStrs.append("None")
return "[ " + " -> ".join(dataListStrs) + " ]"
def push(self, data) -> Stack:
"""Push data that is not NONE onto top of stack,
return stack being pushed.
"""
if data is not None:
node = _Node(data, self._head)
self._head = node
self._count += 1
return self
def pop(self) -> Maybe:
"""Pop data off of top of stack."""
# TODO: chenge to return an Option
if self._head is None:
return Nothing
else:
data = self._head._data
self._head = self._head._next
self._count -= 1
return Some(data)
def head(self) -> Maybe:
"""Returns on option for data at head of stack.
Does not consume the data if it exists.
Returns
-------
data : Some(~None) | Nothing
"""
if self._head is None:
return Nothing
return Some(self._head._data)
def tail(self) -> Maybe:
"""Get the tail of the stack. In the case of an empty stack,
return a stackNONE. This will allow the returned value to be
used as an iterator.
Returns
-------
stack : 'Maybe[Stack]'
"""
if self._head:
stack = Stack()
stack._head = self._head._next
stack._count = self._count - 1
return Some(stack)
return Nothing
def cons(self, data) -> Stack:
"""Return a new stack with data as head and self as tail.
Note that trying to push None on the stack results in a shallow
copy of the original stack.
Returns
-------
stack : 'stack'
"""
if data is not None:
stack = Stack()
stack._head = _Node(data, self._head)
stack._count = self._count + 1
return stack
else:
return self.copy()
def copy(self) -> Stack:
"""Return a shallow copy of the stack in O(1) time & space complexity"""
stack = Stack()
stack._head = self._head
stack._count = self._count
return stack
if __name__ == "__main__":
pass
Classes
class Stack (*data)
-
Class implementing a Last In, First Out (LIFO) stack datastructure. The stack contains a singularly linked list of nodes.
- The stack points to either the top node in the list, or to None to indicate an empty stack.
- Stacks are stateful objects where values can be pushed on & popped off.
- None represents the absence of a value and are ignored if pushed on the stack.
Parameters
*data : 'any' Any data to prepopulate the stack. The data is pushed onto the stack left to right. None values are ignored and not pushed on stack.
Expand source code
class Stack(): """Class implementing a Last In, First Out (LIFO) stack datastructure. The stack contains a singularly linked list of nodes. - The stack points to either the top node in the list, or to None to indicate an empty stack. - Stacks are stateful objects where values can be pushed on & popped off. - None represents the absence of a value and are ignored if pushed on the stack. """ def __init__(self, *data): """ Parameters ---------- *data : 'any' Any data to prepopulate the stack. The data is pushed onto the stack left to right. None values are ignored and not pushed on stack. """ self._head = None self._count = 0 for datum in data: if datum is not None: node = _Node(datum, self._head) self._head = node self._count += 1 def __len__(self): """Returns current number of values on the stack""" return self._count def isEmpty(self) -> bool: """Test if stack is empty""" return self._count == 0 def __iter__(self): """Iterator yielding data stored in the stack, does not consume data.""" node = self._head while node: yield node._data node = node._next def __eq__(self, other): """ Returns True if all the data stored on the two stacks are the same. Worst case is O(n) behavior which happens when all the corresponding data elements on the two stacks are equal, in whatever sense they define equality, and none of the nodes are shared. Parameters ---------- other : 'any' """ if not isinstance(other, type(self)): return False if self._count != other._count: return False left = self right = other nn = self._count while nn > 0: if left is None or right is None: return True if left._head is right._head: return True if left.head() != right.head(): return False left = left.tail().getOrElse(Stack()) right = right.tail().getOrElse(Stack()) nn -= 1 return True def __repr__(self): """Display the data in the stack.""" dataListStrs = [] for data in self: dataListStrs.append(repr(data)) dataListStrs.append("None") return "[ " + " -> ".join(dataListStrs) + " ]" def push(self, data) -> Stack: """Push data that is not NONE onto top of stack, return stack being pushed. """ if data is not None: node = _Node(data, self._head) self._head = node self._count += 1 return self def pop(self) -> Maybe: """Pop data off of top of stack.""" # TODO: chenge to return an Option if self._head is None: return Nothing else: data = self._head._data self._head = self._head._next self._count -= 1 return Some(data) def head(self) -> Maybe: """Returns on option for data at head of stack. Does not consume the data if it exists. Returns ------- data : Some(~None) | Nothing """ if self._head is None: return Nothing return Some(self._head._data) def tail(self) -> Maybe: """Get the tail of the stack. In the case of an empty stack, return a stackNONE. This will allow the returned value to be used as an iterator. Returns ------- stack : 'Maybe[Stack]' """ if self._head: stack = Stack() stack._head = self._head._next stack._count = self._count - 1 return Some(stack) return Nothing def cons(self, data) -> Stack: """Return a new stack with data as head and self as tail. Note that trying to push None on the stack results in a shallow copy of the original stack. Returns ------- stack : 'stack' """ if data is not None: stack = Stack() stack._head = _Node(data, self._head) stack._count = self._count + 1 return stack else: return self.copy() def copy(self) -> Stack: """Return a shallow copy of the stack in O(1) time & space complexity""" stack = Stack() stack._head = self._head stack._count = self._count return stack
Methods
def cons(self, data) ‑> Stack
-
Return a new stack with data as head and self as tail. Note that trying to push None on the stack results in a shallow copy of the original stack.
Returns
stack
:'stack'
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def cons(self, data) -> Stack: """Return a new stack with data as head and self as tail. Note that trying to push None on the stack results in a shallow copy of the original stack. Returns ------- stack : 'stack' """ if data is not None: stack = Stack() stack._head = _Node(data, self._head) stack._count = self._count + 1 return stack else: return self.copy()
def copy(self) ‑> Stack
-
Return a shallow copy of the stack in O(1) time & space complexity
Expand source code
def copy(self) -> Stack: """Return a shallow copy of the stack in O(1) time & space complexity""" stack = Stack() stack._head = self._head stack._count = self._count return stack
def head(self) ‑> Maybe
-
Returns on option for data at head of stack. Does not consume the data if it exists.
Returns
data
:Some(~None) | Nothing
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def head(self) -> Maybe: """Returns on option for data at head of stack. Does not consume the data if it exists. Returns ------- data : Some(~None) | Nothing """ if self._head is None: return Nothing return Some(self._head._data)
def isEmpty(self) ‑> bool
-
Test if stack is empty
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def isEmpty(self) -> bool: """Test if stack is empty""" return self._count == 0
def pop(self) ‑> Maybe
-
Pop data off of top of stack.
Expand source code
def pop(self) -> Maybe: """Pop data off of top of stack.""" # TODO: chenge to return an Option if self._head is None: return Nothing else: data = self._head._data self._head = self._head._next self._count -= 1 return Some(data)
def push(self, data) ‑> Stack
-
Push data that is not NONE onto top of stack, return stack being pushed.
Expand source code
def push(self, data) -> Stack: """Push data that is not NONE onto top of stack, return stack being pushed. """ if data is not None: node = _Node(data, self._head) self._head = node self._count += 1 return self
def tail(self) ‑> Maybe
-
Get the tail of the stack. In the case of an empty stack, return a stackNONE. This will allow the returned value to be used as an iterator.
Returns
stack
:'Maybe[Stack]'
Expand source code
def tail(self) -> Maybe: """Get the tail of the stack. In the case of an empty stack, return a stackNONE. This will allow the returned value to be used as an iterator. Returns ------- stack : 'Maybe[Stack]' """ if self._head: stack = Stack() stack._head = self._head._next stack._count = self._count - 1 return Some(stack) return Nothing