https://leetcode.com/problems/two-sum
Given an array of integers, return indices of the two numbers such that they add up to a specific target.
https://leetcode.com/problems/maximum-subarray/
Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.
https://leetcode.com/problems/maximum-product-subarray/
Given an integer array nums, find the contiguous subarray within an array (containing at least one number) which has the largest product.
https://leetcode.com/problems/valid-parentheses/
Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
5. Best Time to Buy and Sell Stock
https://leetcode.com/problems/best-time-to-buy-and-sell-stock/
Say you have an array for which the ith element is the price of a given stock on day i.
If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm to find the maximum profit.
https://leetcode.com/problems/house-robber/
Given a list of non-negative integers representing the amount of money of each house, determine the maximum amount of money you can rob tonight without alerting the police.
https://leetcode.com/problems/range-sum-of-bst/
https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/
https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/
https://leetcode.com/problems/merge-two-binary-trees/
https://leetcode.com/problems/flatten-binary-tree-to-linked-list/
12. FlattenMultilevelLinkedList
https://leetcode.com/problems/flatten-a-multilevel-doubly-linked-list/
https://leetcode.com/problems/search-in-a-binary-search-tree/
https://leetcode.com/problems/gas-station/
https://leetcode.com/problems/is-subsequence/
https://leetcode.com/problems/binary-watch/
https://leetcode.com/problems/letter-case-permutation/
https://leetcode.com/problems/remove-element
19. Remove Duplicates from Sorted Array
https://leetcode.com/problems/remove-duplicates-from-sorted-array/
https://leetcode.com/problems/n-queens/
21. Replace Elements with Greatest Element on Right Side
https://leetcode.com/problems/replace-elements-with-greatest-element-on-right-side/