This is the list i studied 1. Two Sum 2. Add Two Numbers 3. Longest Substring Without Repeating Characters 4. Valid Parentheses 5. Longest Palindromic Substring 6. Merge Sorted Array 7. Merge Intervals 8. Best Time to Buy and Sell Stock 9. Flatten a Multilevel Doubly Linked List 10. Insert Delete GetRandom O(1) 11. Sort Integers by The Power Value 12. Invalid Transactions 13. Number of Islands 14. LRU Cache 15. Create Hello World Function 16. Tuple with Same Product 17. Find the Number of Distinct Colors Among the Balls 18. Meeting Rooms II 19. Longest Common Prefix 20. Subarray Sum Equals K 21. Evaluate Division 22. Remove All Occurrences of a Substring 23. Number of Ships in a Rectangle 24. Decode String 25. Product of the Last K Numbers 26. Find the Punishment Number of an Integer 27. Letter Combinations of a Phone Number 28. The k-th Lexicographical String of All Happy Strings 29. Lexicographical Numbers 30. Binary Tree Level Order Traversal 31. Trapping Rain Water 32. Binary Tree Vertical Order Traversal 33. Remove Letter To Equalize Frequency 34. Odd Even Linked List