stack code

Author: greyshell

ds_algorithm/stack/demo_stack.py

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+# !/usr/bin/env python3
+
+# author: greyshell
+# description: stack using list
+
+
+def main():
+    """
+    - python list is backed by dynamic array, so occasionally it needs to be resized when item is added / removed
+    - it does not guarantee the stable O(1) push and pop
+    - however, it provides the amortize time complexity is O(1) when the item is added / remove at the end of list
+    - adding / removing from front is much slower and it takes O(n) time as shifting of existing elements are required
+    - IndexError => pop from an empty list
+    - no parallel processing support / it handles locking and unlocking
+    :return:
+    """
+    s = list()
+    # push: O(1), stack grows from left to right
+    s.append(9)
+    s.append(5)
+    s.append(3)
+    s.append(2)
+
+    # display the stack elements
+    print(f"display the stack elements: {s}")
+
+    # peek, O(1)
+    data = s[-1]
+    print(f"peek the stack top: {data}")
+
+    # pop: O(1), stack shrinks from right to left
+    data = s.pop()
+    print(f"popped: {data}")
+
+    print(f"display the stack elements: {list(s)}")
+
+
+if __name__ == '__main__':
+    main()

ds_algorithm/stack/test/testlib_stack.py

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+#!/usr/bin/env python3
+
+# author: greyshell
+# description: stack using deque
+
+from collections import deque
+
+
+def main():
+    """
+    - deque is backed by doubly linked list
+    - it that guarantees the stable O(1) push and pop
+    - IndexError => pop from an empty list
+    - no parallel processing support / it handles locking and unlocking
+    :return:
+    """
+    s = deque()
+    # push: O(1), stack grows from left to right
+    s.append(9)
+    s.append(5)
+    s.append(3)
+    s.append(1)
+
+    # display the stack elements: convert the deque into list
+    print(f"display the stack elements: {s}")
+    print(f"display the stack elements: {list(s)}")
+
+    # peek, O(1)
+    data = s[-1]
+    print(f"peek the stack top: {data}")
+
+    # pop: O(1), stack shrinks from right to left
+    data = s.pop()
+    print(f"popped: {data}")
+
+    print(f"display the stack elements: {list(s)}")
+
+
+if __name__ == '__main__':
+    main()

ds_algorithm/stack/test/testlib_stack02.py

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+#!/usr/bin/env python3
+
+# author: greyshell
+# description: stack using queue.LifoQueue
+
+from queue import LifoQueue
+
+
+def main():
+    """
+    - used for parallel computing / multi producer and consumer scenarios
+    - locking and un-locaking needs to be implemented manually
+    :return:
+    """
+    s = LifoQueue()
+    # push: O(1)
+    s.put(9)
+    s.put(2)
+
+    # check if the stack is empty
+    print(f"{s.empty()}")
+
+    # not found any method for peek and display stack elements
+
+    # pop: O(1)
+    data = s.get_nowait()  # not wait for producer to add the element if the stack is empty
+    print(f"popped: {data}")
+
+    data = s.get()  # poped out the last stack element
+    data = s.get()  # waits for ever as the stack is empty, producer needs to add an element
+    print(f"popped: {data}")
+
+
+if __name__ == '__main__':
+    main()