1. Implement a function to find the smallest element in a stack in O(1) time.
2. Write a function to reverse a stack using recursion.
3. Implement a stack that supports push, pop, top, and retrieving the minimum element in constant time.
4. Write a function to evaluate a mathematical expression in postfix notation with error handling.
5. Implement a function to sort a stack using another stack.
6. Write a function to check if a stack is a permutation of another stack.
7. Implement a function to find the longest valid parentheses substring in a string using a stack.
8. Write a function to implement a priority stack that retrieves the highest priority item.
9. Implement a function to calculate the maximum depth of nested parentheses.
10. Write a function to implement a two-stack queue.
11. Implement a function to check if a stack can be sorted with a limited number of auxiliary stacks.
12. Write a function to create a stack that keeps track of the maximum element.
13. Implement a function to find the longest common subsequence between two strings using a stack.
14. Write a function to implement a min-max stack.
15. Implement a function to find all valid combinations of parentheses using a stack.
16. Write a function to detect a cycle in a stack representation of a linked list.
17. Implement a function to evaluate infix expressions using the Shunting Yard algorithm.
18. Write a function to check if a stack is a palindrome.
19. Implement a function to merge K sorted stacks into a single sorted stack.
20. Write a function to find the shortest valid parentheses substring.
21. Implement a function to implement a stack that supports duplicate elements while maintaining order.
22. Write a function to find the longest substring without repeating characters using a stack.
23. Implement a function to create a stack that supports range queries.
24. Write a function to find the number of ways to arrange parentheses.
25. Implement a function to find the maximum area of a rectangle in a histogram using a stack.
26. Write a function to evaluate a complex expression with nested operations.
27. Implement a function to check if a string is a valid serialization of a binary tree using a stack.
28. Write a function to calculate the longest increasing subsequence in a stack.
29. Implement a function to generate all possible permutations of a stack using backtracking.
30. Write a function to find the maximum difference between the top two elements of a stack.
31. Implement a function to create a stack of infinite capacity.
32. Write a function to find the maximum sum of a contiguous subarray in a stack.
33. Implement a function to validate a binary search tree using a stack.
34. Write a function to implement a stack that can undo operations.
35. Implement a function to flatten a nested stack.
36. Write a function to find the shortest path in a maze using a stack.
37. Implement a function to calculate the total number of valid configurations of a stack.
38. Write a function to find the longest balanced substring of brackets using a stack.
39. Implement a function to evaluate a postfix expression with multiple operators.
40. Write a function to create a stack that maintains the insertion order of elements.