| Problem | Reason | Reference |
| Moving Zeroes Sort Colors |
Corner cases | |
| Shortest Word Distance | Thought: 2 ptr chasing | |
| Merge 2 sorted Lists Remove Linked List Elem |
Corner cases | |
| Power of Four | Thought: fun bit ops | |
| Pow(x, n) | int overflow | |
| Rectangle Area | Thought | |
| Merge Sorted Array | Thought: from the back | |
| Count Primes | Corner cases | |
| First Bad Version | Corner cases | |
| Rotate Array | Thought: Multiple solutions | |
| Counting Bits | Thought: Fun DP | |
| Top K Frequent Elements | Thought: BUCKETING! | |
| Isomorphic Strings | Thought: note - bidirectional | |
| Excel Sheet Column Title | Thought: list first several cases | |
| Bulb Switcher | MathBrainteaser | |
| Word Pattern | Corner case | |
| Majority Number | Thought: counting strategy | More thoughts |
| Add Digits | Math, or by samples | LC Forum |
| Power of 3 | Math | LC Forum |
| Factorial Trailing Zeros | Mathcounting | |
| Generate Parentheses | DFS fun | |
| Longest Inc Path in Matrix | DFS + Memorized Search | |
| Binary Tree Inorder Traversal | DFS->Iterative | LC Forum |
| Reverse Words in a String | Note the copy trick! | LC Forum |
| House Robber | DP: fun ! | |
| Paint Fence | DP: fun ! | |
| Binary Search Tree Iterator | StackIterator | |
| Count Numbers with Unique Digits | Math: Combinatorics | |
| Combinations | Note the backtracking one | |
| Min Stack | Stack. Fun | |
| Integer Break | DP, and Math | |
| strStr() | *KMP algo. |