Stcak using Linked List

Author: noviicee

Code/Python/stack_using_linked_list.py

@@ -0,0 +1,155 @@
+"""Problem Description:
+Implementation of stack using Linked List.
+
+A stack can be easily implemented through linked list.
+In this implementation,
+the top pointer of the stack is “head” of the linked list where pushing and popping items take place.
+First node have null in link field and second node link have first node address in link field.
+It continues so on and last node address in “top” pointer.
+
+The main advantage of using linked list over an arrays in stack implementation is-
+it can shrink or grow as much as needed unlike fixed size of array
+
+The main Stack Operations are:
+
+->push() : Insert the element into linked list nothing but which is the top node of Stack.
+->pop() : Return top element from the Stack and move the top pointer to the second node of linked list or Stack.
+->peek()/top(): Return the top element.
+->display(): Print all element of Stack.
+
+[Reference for Description]->(https://www.geeksforgeeks.org/implement-a-stack-using-singly-linked-list/)
+"""
+
+
+class Node:
+    def __init__(self, data):
+        self.data = data
+        self.ref = None
+
+
+class Stack:
+    def __init__(self):
+        self.__head = None
+        self.__size = 0
+
+    def push(self, data):
+        # adds an element at the beginning
+        self.__size += 1
+        new_node = Node(data)
+        new_node.ref = self.__head
+        self.__head = new_node
+
+    def pop(self):
+        # deletes element from beginning
+        if self.isEmpty():
+            print("Stack is empty.")
+            return
+        self.__size -= 1
+        print(self.__head.data)
+        self.__head = self.__head.ref
+
+    def top(self):
+        # prints the topmost element, i.e, head in the case of LL
+        if self.isEmpty():
+            print("Stack is empty.")
+            return
+        print(self.__head.data)
+
+    def isEmpty(self):
+        return(self.__size == 0)
+
+    def display(self):
+        # displays the stack from top to bottom
+        n = self.__head
+        if n is None:
+            print("Empty!")
+            return
+        while n is not None:
+            print(n.data)
+            n = n.ref
+
+
+if __name__ == "__main__":
+    s2 = Stack()
+    print("Enter values to push in the stack: ")
+    value = [ele for ele in input().split()]
+    for i in range(len(value)):
+        s2.push(value[i])
+    print("The stack is:")
+    s2.display()
+    print('\nThe first element which is removed is: ')
+    s2.pop()
+    print('\nThe topmost element of the stack is:')
+    s2.top()
+    print("\nThe stack is:")
+    s2.display()
+
+
+"""Time-Complexity of the program:
+push(): O(1)
+pop(): O(1)
+top(): O(1)
+display(): O(N)
+"""
+
+"""Test-Cases:
+
+>>>
+Enter values to push in the stack:
+10 15 23 42
+The stack is:
+42
+23
+15
+10
+
+The first element which is removed is:
+42
+
+The topmost element of the stack is:
+23
+
+The stack is:
+23
+15
+10
+
+>>>
+Enter values to push in the stack:
+Anamika
+The stack is:
+Anamika
+
+The first element which is removed is:
+Anamika
+
+The topmost element of the stack is:
+Stack is empty.
+
+The stack is:
+Empty!
+
+>>>
+Enter values to push in the stack:
+Anamika 1 QWERTY 22 key 87
+The stack is:
+87
+key
+22
+QWERTY
+1
+Anamika
+
+The first element which is removed is:
+87
+
+The topmost element of the stack is:
+key
+
+The stack is:
+key
+22
+QWERTY
+1
+Anamika
+"""

Stack/readme.md

@@ -28,4 +28,5 @@ element in a full stack is called **overflow**.
 -   Largest Rectangle ----> [C++](/Code/C++/Largest_Rectangle.cpp)
 -   Reverse individual words of a string ----> [C++](/Code/C++/reverse_words_of_string.cpp)
 -   Stack Class ----> [C++](/Code/C++/stack_class.cpp)
+-   Stack using Linked List ----> [Python](/Code/Python/stack_using_linked_list.py)
 -   Stock Span Problem ----> [C++](/Code/C++/Stock_Span_Problem.cpp) | [Java](/Code/Java/Stock_Span_Problem.Java) | [Python](/Code/Python/StockSpan.py)