| 075 | [Sort Colors](https://github.com/interviewcoder/leetcode/blob/master/src/_075_SortColors/Solution.java) | Medium | `Array` `Two Pointers` `Sort` | |

| 076 | [Minimum Window Substring](https://github.com/interviewcoder/leetcode/blob/master/src/_076_MinimumWindowSubstring/Solution.java) | Hard | `Hash Table` `Two Pointers` `String` | `!`**[substring/sublist]** hashing + two pointers -> O(N) |

| 077 | [Combinations](https://github.com/interviewcoder/leetcode/blob/master/src/_077_Combinations/Solution.java) | Medium | `Backtracking` | |

| 079 | [Word Search](https://github.com/interviewcoder/leetcode/blob/master/src/_079_WordSearch/Solution.java) | Medium | `Array` `Backtracking` | |

| 080 | [Remove Duplicates from Sorted Array II](https://github.com/interviewcoder/leetcode/blob/master/src/_080_RemoveDuplicatesFromSortedArrayII/) | Medium | `Array` `Two Pointers` | from 2 to k (general) |

| 081 | [Search in Rotated Sorted Array II](https://github.com/interviewcoder/leetcode/blob/master/src/_081_SearchInRotatedSortedArrayII/Solution.java) | Medium | `Array` `Binary Search` | |

| 123 | [Best Time to Buy and Sell Stock III](https://github.com/interviewcoder/leetcode/blob/master/src/_123_BestTimeToBuyAndSellStockIII/Solution.java) | Hard | `Array` `Dynamic Programming` | |

| 124 | [Binary Tree Maximum Path Sum](https://github.com/interviewcoder/leetcode/blob/master/src/_124_BinaryTreeMaximumPathSum/) | Hard | `Tree` `Depth-first Search` | post-order, local and global , [README](https://github.com/interviewcoder/leetcode/tree/master/src/_124_BinaryTreeMaximumPathSum) |

| 125 | [Valid Palindrome](https://github.com/interviewcoder/leetcode/blob/master/src/_125_ValidPalindrome/Solution.java) | Easy | `Two Pointers` `String` | |

| 128 | [Longest Consecutive Sequence](https://github.com/interviewcoder/leetcode/blob/master/src/_128_LongestConsecutiveSequence/Solution.java) | Hard | `Array` | |

| 129 | [Sum Root to Leaf Numbers](https://github.com/interviewcoder/leetcode/blob/master/src/_129_SumRootToLeafNumbers/Solution.java) | Medium | `Tree` `Depth-first Search` | |

| 130 | [Surrounded Regions](https://github.com/interviewcoder/leetcode/blob/master/src/_130_SurroundedRegions/Solution.java) | Medium | `Breadth-first Search` | |

| 160 | [Intersection of Two Linked Lists](https://github.com/interviewcoder/leetcode/blob/master/src/_160_IntersectionOfTwoLinkedLists/Solution.java) | Easy | `Linked List` | two pointers on two lists; combine long and short lists into one |

| 161 | [One Edit Distance](https://github.com/interviewcoder/leetcode/blob/master/src/_161_OneEditDistance/) | Medium | `String` | |

| 162 | [Find Peak Element](https://github.com/interviewcoder/leetcode/blob/master/src/_162_FindPeakElement/Solution.java) | Medium | `Array` `Binary Search` | |

| 164 | [Maximum Gap](https://github.com/interviewcoder/leetcode/blob/master/src/_164_MaximumGap/Solution.java) | Hard | `Sort` | |

| 165 | [Compare Version Numbers](https://github.com/interviewcoder/leetcode/blob/master/src/_165_CompareVersionNumbers/Solution.java) | Easy | `String` | |

| 166 | [Fraction to Recurring Decimal](https://github.com/interviewcoder/leetcode/blob/master/src/_166_FractionToRecurringDecimal/Solution.java) | Medium | `Hash Table` `Math` | |

| 282 | Expression Add Operators | Hard | `Divide and Conquer` | |

| 283 | [Move Zeroes](https://github.com/interviewcoder/leetcode/blob/master/src/_283_MoveZeroes/Solution.java) | Easy | `Array` `Two Pointers` | |

| 284 | Peeking Iterator | Medium | `Design` | |

| 286 | [Walls And Gates](https://github.com/interviewcoder/leetcode/tree/master/src/_286_WallsAndGates) | Medium | `BFS` | |

| 287 | Find the Duplicate Number | Hard | `Array` `Two Pointers` `Binary Search` | |

0. [Partition](https://github.com/interviewcoder/leetcode/blob/master/doc/category_partition.md)

| 1 sequence : `max`/min(*) | 032 | [Longest Valid Parentheses](https://github.com/interviewcoder/leetcode/tree/master/src/_032_LongestValidParentheses) | global V.S. local |

| 1 sequence : `max`/min(*) | 121 | Best Time to Buy and Sell Stock | |

| 1 sequence : `max`/min(*) | 123 | Best Time to Buy and Sell Stock III | |

| 1 sequence : all(*) | 140 | Word Break II: dp + backtracking | |

| `continuous` | | continuous subarray | |

| Two Pointers : maxsize | 005 | [Longest Palindromic Substring](https://github.com/interviewcoder/leetcode/blob/master/src/_005_LongestPalindromicSubstring/Solution.java) | O(N^3) -> O(N^2) |

| Two Pointers : maxsize| 003 | [Longest Substring Without Repeating Characters](https://github.com/interviewcoder/leetcode/blob/master/src/_003_LongestSubstringWithoutRepeatingCharacters/Solution.java) | O(N^3) -> O(N) + O(N) hash|

| Two Pointers : minsize | 076 | [Minimum Window Substring](https://github.com/interviewcoder/leetcode/tree/master/src/_076_MinimumWindowSubstring) | O(N^3) -> O(N) + O(N) hash |

| Two Pointers : minsize | 209 | [Minimum Size Subarray Sum](https://github.com/interviewcoder/leetcode/tree/master/src/_209_MinimumSizeSubarraySum) | O(N^3) -> O(N) |

1. Iterative

1.1) Use stack to simulate recursive DFS

1.2) BFS with queue

2.1) visit root first = pre-order = top-down = preorder traversal

2.2) visit root last = post-order = bottom-up = divide and conquer

| level traversal | 103 | Binary Tree Zigzag Level Order Traversal |

| **`Tree::divide and conquer`** | | |

| *`post`*-order | 124 | [Binary Tree Maximum Path Sum](https://github.com/interviewcoder/leetcode/tree/master/src/_124_BinaryTreeMaximumPathSum) |

| *`post`*-order | 104 | [Maximum Depth Of Binary Tree](https://github.com/interviewcoder/leetcode/tree/master/src/_104_MaximumDepthOfBinaryTree) |

| *`post`*-order | 236 | [Lowest Common Ancestor of Binary Tree](https://github.com/interviewcoder/leetcode/tree/master/src/_236_LowestCommonAncestorOfABinaryTree) |

| **`BST::order matters`** | | |