added implementing stack using two queues

data_structures/stacks/stack_using_two_queues.py

@@ -0,0 +1,85 @@
+from __future__ import annotations
+
+from collections import deque
+from dataclasses import dataclass, field
+
+
+@dataclass
+class StackWithQueues:
+ """
+ https://www.geeksforgeeks.org/implement-stack-using-queue/
+
+ >>> stack = StackWithQueues()
+ >>> stack.push(1)
+ >>> stack.push(2)
+ >>> stack.push(3)
+ >>> stack.peek()
+ 3
+ >>> stack.pop()
+ 3
+ >>> stack.peek()
+ 2
+ >>> stack.pop()
+ 2
+ >>> stack.pop()
+ 1
+ >>> stack.peek() is None
+ True
+ >>> stack.pop()
+ Traceback (most recent call last):
+ ...
+ IndexError: pop from an empty deque
+ """
+
+ main_queue: deque[int] = field(default_factory=deque)
+ temp_queue: deque[int] = field(default_factory=deque)
+
+ def push(self, item: int) -> None:
+ self.temp_queue.append(item)
+ while self.main_queue:
+ self.temp_queue.append(self.main_queue.popleft())
+ self.main_queue, self.temp_queue = self.temp_queue, self.main_queue
+
+ def pop(self) -> int:
+ return self.main_queue.popleft()
+
+ def peek(self) -> int | None:
+ return self.main_queue[0] if self.main_queue else None
+
+
+if __name__ == "__main__":
+ import doctest
+
+ doctest.testmod()
+
+ stack: StackWithQueues | None = StackWithQueues()
+ while stack:
+ print("\nChoose operation:")
+ print("1. Push")
+ print("2. Pop")
+ print("3. Peek")
+ print("4. Quit")
+
+ choice = input("Enter choice (1/2/3/4): ")
+
+ if choice == "1":
+ element = int(input("Enter an integer to push: ").strip())
+ stack.push(element)
+ print(f"{element} pushed onto the stack.")
+ elif choice == "2":
+ popped_element = stack.pop()
+ if popped_element is not None:
+ print(f"Popped element: {popped_element}")
+ else:
+ print("Stack is empty.")
+ elif choice == "3":
+ peeked_element = stack.peek()
+ if peeked_element is not None:
+ print(f"Top element: {peeked_element}")
+ else:
+ print("Stack is empty.")
+ elif choice == "4":
+ del stack
+ stack = None
+ else:
+ print("Invalid choice. Please try again.")