https://www.hackerrank.com/challenges/simple-text-editor/problem

simple_text_editor.py

Q = int(input().strip(' '))
# print(Q)

class Node():
    def __init__(self, val=None, next=None):
        self.val = val
        self.next = next
    
class Stack():
    def __init__(self, head=None):
        self.head = head
    
    def pop(self):
        if self.head:
            node = self.head
            self.head = node.next
            return node.val
        else:
            return None
        
    def push(self, val):
        if self.head:
            self.head = Node(val, self.head)
        else:
            self.head = Node(val, None)
   
class Editor():
    def __init__(self):
        self.states = Stack()
        self.text = ''
        
    def execute(self, operation):
        l = len(self.text)
        parts = operation.split(' ')
        t = int(parts[0])
        
        if t == 1:
            self.states.push(self.text)
            self.text += str(parts[1])
        
        if t == 2:
            self.states.push(self.text)
            k = int(parts[1])
            if k >= l:
                self.text = ''
            else:
                self.text = self.text[:l-k]
                
        if t == 3:
            k = int(parts[1])
            print(self.text[k-1])

        if t == 4:
            self.text = self.states.pop()
        
editor = Editor()    

for i in range(Q):
    operation = input().strip()
    editor.execute(operation)