added stack_using_two_queues.py

data_structures/stacks/stack_using_two_queues.py

@@ -0,0 +1,120 @@
+from collections import deque
+from typing import Optional
+
+
+class StackUsingQueues:
+    def __init__(self) -> None:
+        self.queue1 = deque()
+        self.queue2 = deque()
+
+    def push(self, value: int) -> None:
+        """
+        Pushes an element onto the stack.
+
+        Args:
+            value (int): The element to push onto the stack.
+
+        Example:
+            >>> stack = StackUsingQueues()
+            >>> stack.push(1)
+            >>> stack.push(2)
+            >>> stack.push(3)
+        """
+        self.queue2.append(value)
+        while self.queue1:
+            self.queue2.append(self.queue1.popleft())
+        self.queue1, self.queue2 = self.queue2, self.queue1
+
+    def pop(self) -> None:
+        """
+        Pops and removes the top element from the stack.
+
+        Example:
+            >>> stack = StackUsingQueues()
+            >>> stack.push(1)
+            >>> stack.push(2)
+            >>> stack.pop()
+        """
+        if self.queue1:
+            self.queue1.popleft()
+
+    def top(self) -> Optional[int]:
+        """
+        Returns the top element of the stack without removing it.
+
+        Returns:
+            int: The top element of the stack, or None if the stack is empty.
+
+        Example:
+            >>> stack = StackUsingQueues()
+            >>> stack.push(1)
+            >>> stack.push(2)
+            >>> stack.top()
+            2
+        """
+        if self.queue1:
+            return self.queue1[0]
+        return None
+
+    def size(self) -> int:
+        """
+        Returns the current size (number of elements) of the stack.
+
+        Returns:
+            int: The size of the stack.
+
+        Example:
+            >>> stack = StackUsingQueues()
+            >>> stack.size()
+            0
+            >>> stack.push(1)
+            >>> stack.push(2)
+            >>> stack.push(3)
+            >>> stack.size()
+            3
+            >>> stack.pop()
+            >>> stack.size()
+            2
+        """
+        return len(self.queue1)
+
+    def is_empty(self) -> bool:
+        """
+        Checks if the stack is empty.
+
+        Returns:
+            bool: True if the stack is empty, False otherwise.
+
+        Example:
+            >>> stack = StackUsingQueues()
+            >>> stack.is_empty()
+            True
+            >>> stack.push(1)
+            >>> stack.is_empty()
+            False
+        """
+        return len(self.queue1) == 0
+
+    def peek(self) -> Optional[int]:
+        """
+        Returns the top element of the stack without removing it.
+
+        Returns:
+            int: The top element of the stack, or None if the stack is empty.
+
+        Example:
+            >>> stack = StackUsingQueues()
+            >>> stack.push(1)
+            >>> stack.push(2)
+            >>> stack.peek()
+            2
+        """
+        if self.queue1:
+            return self.queue1[0]
+        return None
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()