# 
Title 
Difficulty 
1 
Add Digits 
Easy 
2 
Add Two Numbers II 
Medium 
3 
Add Two Numbers 
Easy 
4 
Anagrams 
Medium 
5 
Big Integer Addition 
Easy 
6 
Big Integer multiplication 
Medium 
7 
Binary Tree Level Order Traversal 
Easy 
8 
Binary Tree Path Sum 
Easy 
9 
Binary Tree Paths 
Easy 
10 
Classical Binary Search 
Easy 
11 
Climbing Stairs II 
Easy 
12 
Climbing Stairs 
Easy 
13 
Coins in a Line II 
Medium 
14 
Coins in a Line III 
Hard 
15 
Coins in a Line 
Easy 
16 
Connecting Graph 
Medium 
17 
Continuous Subarray Sum 
Medium 
18 
Convert BST to Greater Tree 
Easy 
19 
Cosine Similarity 
Easy 
20 
Count 1 in Binary 
Easy 
21 
Count and Say 
Easy 
22 
Decode Ways 
Medium 
23 
Find K Closest Elements 
Medium 
24 
Find Prime numbers 
Easy 
25 
Find Square numbers 
Easy 
26 
First Position Unique Character 
Easy 
27 
Flatten Binary Tree to Linked List 
Easy 
28 
Guess Number Game 
Easy 
29 
Happy Number 
Easy 
30 
Identical Binary Tree 
Easy 
31 
Intersection of Two Arrays II 
Easy 
32 
Intersection of Two Arrays 
Easy 
33 
Invert Binary Tree 
Easy 
34 
Judge Route Circle 
Easy 
35 
K Closest Points 
Medium 
36 
Left Pad 
Easy 
37 
Length of Last Word 
Easy 
38 
Longest Increasing Continuous Subsequence 
Easy 
39 
Longest Increasing Subsequence 
Medium 
40 
Longest Palindrome 
Easy 
41 
Longest Substring with At Most K Distinct Characters 
Medium 
42 
Longest Words 
Easy 
43 
Lowest Common Ancestor 
Medium 
44 
LRU Cache 
Hard 
45 
Maximum Average Subarray I 
Easy 
46 
Maximum Product of Three Numbers 
Easy 
47 
Maximum Subarray II 
Medium 
48 
Maximum Subarray 
Easy 
49 
Maximum Width of Binary Tree 
Medium 
50 
Merge Sorted Array 
Easy 
51 
Merge Two Sorted Lists 
Easy 
52 
Minimum Depth of Binary Tree 
Easy 
53 
Move Zeroes 
Easy 
54 
O(1) Check Power of 2 
Easy 
55 
Paint Fence 
Easy 
56 
Palindrome Number 
Easy 
57 
Partition Array 
Medium 
58 
Pascal's Triangle II 
Easy 
59 
Plus One 
Easy 
60 
Remove 9 
Hard 
61 
Reverse Linked List II 
Medium 
62 
Reverse Linked List 
Easy 
63 
Reverse Pairs 

64 
Reverse Words in a String 

65 
Scramble String 
Hard 
66 
Search for a Range 
Medium 
67 
Second Max of Array 

68 
Singleton 

69 
Sort Integers II 

70 
Space Replacement 

71 
Split Array into Consecutive Subsequences 
Medium 
72 
String Permutation 

73 
Strings Homomorphism 

74 
Substring Anagrams 
Easy 
75 
Swap Bits 
Easy 
76 
Swap Nodes in Pairs 

77 
Toy Factory 

78 
Two Strings Are Anagrams 

79 
Two Sum 
Easy 
80 
Ugly Number 

81 
Valid Number 
Hard 
82 
Valid Palindrome 

83 
Valid Parentheses 

84 
Word Count (Map Reduce) 
