simple stack

Author: hashfx

DSA-Python/DataStructures/stack.py

@@ -0,0 +1,73 @@
+''' 
+STACK
+    LIFO
+
+All push and pop operations are to/from the top of the stack
+    PUSH an item onto the stack
+    POP an item off of the stack
+    PEEK to get item on top of stack, without removing it
+    CLEAR all items from stack
+
+STACK USE CASE
+Undo Command : track which command have been executed. Pop last command off the command stack to undo it
+Calling Function: Function Calling in any programming language is managed using stack
+
+Stack Class in Python:
+    list
+    collections.deque
+    queue.LifoQueue
+
+BigO of stack:
+    Push/Pop element -----> O(1)
+    Search element by value -----> O(n)
+
+'''
+
+''' CLASS STACK() '''
+class Stack():
+    def __init__(self):
+        self.stack = list()
+
+    def push(self, item):
+        self.stack.append(item)
+
+    def pop(self):
+        if len(self.stack) > 0:
+            return self.stack.pop()
+
+    def peek(self):
+        if len(self.stack) > 0:
+            return self.stack[len(self.stack)-1]
+        else:
+            return None
+
+    def __str__(self):
+        return str(self.stack)
+''' CLASS STACK() END '''        
+
+stack = list()
+# .append method to append items to the stack
+stack.append(1)
+stack.append(4)
+stack.append(9)
+stack.append(16)
+print(f"Stack is {stack}", end="\n\n")
+stack.pop()
+print(f"Deleted Last item of Stack (LIFO) {stack}", end="\n\n")
+
+# Calling Stack() class
+stack = Stack()
+
+stack.push(1)
+stack.push(2)
+stack.push(3)
+stack.push('B')
+
+print(f"New Stack is {stack}")
+print(f"Deleted item is {stack.pop()}")
+print(f"Seek is at {stack.peek()}")
+
+
+
+#TODO: Stack continue ( https://youtu.be/kQDxmjfkIKY?t=3077 )
+