Add new Amazon SDE-1 questions from leetcode

[santhoshvai]

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See https://leetcode.com/discuss/interview-question/488887/amazon-final-interview-questions-sde1

* not required to solve
~ solve both iteratively and recursively

• [x] Two Sum Easy
• [ ] Median of Two Sorted Arrays * (#4)
• [ ] Longest Palindromic Substring (#5)
• [ ] String to Integer (atoi) (#8)
• [ ] Integer to Roman (#12)
• [ ] Roman to Integer (#13)
• [ ] Valid Parentheses (#20)
• [ ] Merge K Sorted Lists (#23)
• [ ] Valid Sudoku (#36)
• [ ] Combination Sum (#39)
• [ ] Permutations (#46)
• [x] Merge Intervals Medium
• [ ] Rotate List (#61)
• [ ] Word Search (#79)
• [ ] Validate Binary Search Tree(#98)
• [ ] Same Tree ~ (#100)
• [ ] Symmetric Tree ~ (#101)
• [ ] Binary Tree Level Order Traversal (#102)
• [ ] Convert Sorted List to Binary Search Tree (#109)
• [ ] Populating Next Right Pointers in Each Node (#116)
• [x] Best Time to Buy and Sell Stock Easy
• [ ] Word Ladder II (#126)
• [ ] Word Ladder (#127)
• [ ] LRU Cache (#146)
• [ ] Min Stack (#155)
• [ ] Number of Islands (#200)
• [ ] Course Schedule (#207)
• [ ] Course Schedule II (#210)
• [ ] Integer to English Words (#273)
• [ ] Game of Life (#289)
• [ ] Find Median from Data Stream (#295)
• [ ] Longest Increasing Subsequence (#300)
• [ ] Design Tic-Tac-Toe (#348)
• [ ] Pacific Atlantic Water Flow (#417)
• [ ] Minesweeper (#529)
• [ ] Diameter of Binary Tree (#543)
• [ ] Reorganize String (#767)