Add: Queue using Stacks Implementation in Python

[saishmungase]

Description

This PR adds an implementation of a FIFO Queue data structure using two LIFO Stacks, as requested in the data_structures README (High Priority).

• File Added: Python/data_structures/queue/queue_using_stacks.py
• Functionality: Implements enqueue, dequeue, peek, is_empty, size using two internal lists (_in_stack, _out_stack) to simulate FIFO behavior.
• Follows FIFO principle with amortized O(1) dequeue/peek.

Algorithm Description (Included in code comments)

Elements are enqueued onto _in_stack. Dequeue/peek operations transfer elements from _in_stack to _out_stack (reversing them) only when _out_stack is empty, then operate on _out_stack.

Complexity Analysis (Included in code comments)

• Time Complexity:
  • Enqueue: O(1)
  • Dequeue: O(1) amortized
  • Peek: O(1) amortized
• Space Complexity: O(n)

Checklist

• Code follows the project's contributing guidelines (folder structure, naming).
• Code includes data structure description comment.
• Code includes time and space complexity analysis.
• Code is tested (includes doctests).
• Commit message follows the specified format.
• This PR adds one specific data structure implementation.

[github-actions]

🎉 Welcome to Hacktoberfest 2025, @saishmungase! 🎃

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[github-actions]

🤖 Automated PR Status

🔍 Code Validation

✅ Passed - File naming and structure look good!

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✅ Passed - All code compiles successfully!

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[saishmungase]

Hey @Pradeepsingh61 , @Karanjot786 Can You Please check this PR ?