# Source code for algorithms.data_structures.stack

"""
Stack
-----
A stack or LIFO (last in, first out) is an abstract data type that serves
as a collection of elements, with two principal operations: push, which
adds an element to the collection, and pop, which removes the last element
that was added.
Pseudo Code: https://en.wikipedia.org/wiki/Stack_%28abstract_data_type%29
"""
[docs]class Stack:
def __init__(self):
self.stack_list = []
[docs] def add(self, value):
"""
Add element at last
Time Complexity: O(1)
"""
self.stack_list.append(value)
[docs] def remove(self):
"""
Remove element from last return value
Time Complexity: O(1)
"""
return self.stack_list.pop()
[docs] def is_empty(self):
"""
1 value returned on empty 0 value returned on not empty
Time Complexity: O(1)
"""
return not self.size()
[docs] def size(self):
"""
Return size of stack
Time Complexity: O(1)
"""
return len(self.stack_list)