Stack

1. What is Stack?
2. Stack Types
3. Stack Operations
4. Applications of Stack
5. Practice Problems
• Implement Stack from Scratch
• Implement Queue from Scratch
• Implement 2 stack in an array
• Find the middle element of a stack
• Implement "N" stacks in an Array
• Check the expression has valid or Balanced parenthesis or not.
• Reverse a String using Stack
• Design a Stack that supports getMin() in O(1) time and O(1) extra space.
• Find the next Greater element
• The celebrity Problem
• Arithmetic Expression evaluation
• Evaluation of Postfix expression
• Implement a method to insert an element at its bottom without using any other data structure.
• Reverse a stack using recursion
• Sort a Stack using recursion
• Merge Overlapping Intervals
• Largest rectangular Area in Histogram
• Length of the Longest Valid Substring
• Expression contains redundant bracket or not
• Implement Stack using Queue
• Implement Stack using Deque
• Stack Permutations (Check if an array is stack permutation of other)
• Implement Queue using Stack  
• Implement "n" queue in an array
• Implement a Circular queue
• LRU Cache Implementationa
• Reverse a Queue using recursion
• Reverse the first “K” elements of a queue
• Interleave the first half of the queue with second half
• Find the first circular tour that visits all Petrol Pumps
• Minimum time required to rot all oranges
• Distance of nearest cell having 1 in a binary matrix
• First negative integer in every window of size “k”
• Check if all levels of two trees are anagrams or not.
• Minimum sum of squares of character counts in a given string after removing “k” characters.
• Queue based approach or first non-repeating character in a stream.
• Next Smaller Element