【1】Two Sum 

【3】Longest Substring Without Repeating Characters 

【18】4Sum 

【30】Substring with Concatenation of All Words 

【36】Valid Sudoku 

【37】Sudoku Solver 

【49】Group Anagrams 

【76】Minimum Window Substring 

【85】Maximal Rectangle 

【94】Binary Tree Inorder Traversal 

【136】Single Number 

【138】Copy List with Random Pointer 

【149】Max Points on a Line 

【159】Longest Substring with At Most Two Distinct Characters 

【166】Fraction to Recurring Decimal 

【170】Two Sum III - Data structure design 

【187】Repeated DNA Sequences 

【202】Happy Number 

【204】Count Primes 

【205】Isomorphic Strings 

【217】Contains Duplicate 

【219】Contains Duplicate II 

【242】Valid Anagram 

【244】Shortest Word Distance II 

【246】Strobogrammatic Number 

【249】Group Shifted Strings 

【266】Palindrome Permutation 

【274】H-Index 

【288】Unique Word Abbreviation 

【290】Word Pattern 

【299】Bulls and Cows 

【311】Sparse Matrix Multiplication 

【314】Binary Tree Vertical Order Traversal 

【325】Maximum Size Subarray Sum Equals k 

【336】Palindrome Pairs 

【340】Longest Substring with At Most K Distinct Characters 

【347】Top K Frequent Elements 

【349】Intersection of Two Arrays 

【350】Intersection of Two Arrays II 

【355】Design Twitter 

【356】Line Reflection 

【358】Rearrange String k Distance Apart 

【359】Logger Rate Limiter 

【380】Insert Delete GetRandom O(1) 

【381】Insert Delete GetRandom O(1) - Duplicates allowed 

【387】First Unique Character in a String 

【389】Find the Difference 

【409】Longest Palindrome 

【438】Find All Anagrams in a String 

【447】Number of Boomerangs 

【451】Sort Characters By Frequency 

【454】4Sum II 

【463】Island Perimeter 

【500】Keyboard Row 

【508】Most Frequent Subtree Sum 

【525】Contiguous Array 

【535】Encode and Decode TinyURL 

【554】Brick Wall 

【560】Subarray Sum Equals K 

【575】Distribute Candies 

【594】Longest Harmonious Subsequence 

【599】Minimum Index Sum of Two Lists 

【609】Find Duplicate File in System 

【624】Maximum Distance in Arrays 

【632】Smallest Range 

【645】Set Mismatch 

【648】Replace Words 

【676】Implement Magic Dictionary 

【690】Employee Importance 

【692】Top K Frequent Words 

【694】Number of Distinct Islands 

【705】Design HashSet 

【706】Design HashMap 

【710】Random Pick with Blacklist 

【711】Number of Distinct Islands II 

【718】Maximum Length of Repeated Subarray 

【720】Longest Word in Dictionary 

【726】Number of Atoms 

【734】Sentence Similarity 

【739】Daily Temperatures 

【748】Shortest Completing Word 

【760】Find Anagram Mappings 

【770】Basic Calculator IV 

【771】Jewels and Stones 

【781】Rabbits in Forest 

【811】Subdomain Visit Count 

【884】Uncommon Words from Two Sentences 

【895】Maximum Frequency Stack