Stacks & Queues Recommended Order By Topic Basic Stack & Queue Questions Order Question Difficulty Votes 1 Min Stack Easy 2 Implement a Queue Using Stacks Easy 3 Implement a Stack Using Queues Easy 4 Design Circular Queue Medium 5 LRU Cache Medium Stacks & Queues + Arrays / Strings Order Question Difficulty Votes 1 Valid Parantheses Easy 2 First Unique Character in a String Easy 3 Minimum Remove to Make Valid Parentheses Medium 4 Daily Temperatures Medium 5 Sliding Window Maximum Hard Stacks & Queues + Trees / Graphs Order Question Difficulty Votes 1 Clone Graph Medium 2 Level Order Traversal Medium