|301|[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)|[Solution](../master/src/main/java/com/stevesun/solutions/RemoveInvalidParentheses.java)| ? | ? | Hard| BFS

|299|[Bulls and Cows](https://leetcode.com/problems/bulls-and-cows/)|[Solution](../master/src/main/java/com/stevesun/solutions/BullsandCows.java)| O(n)|O(1) | Easy|

|298|[Binary Tree Longest Consecutive Sequence](https://leetcode.com/problems/binary-tree-longest-consecutive-sequence/)|[Solution](../master/src/main/java/com/stevesun/solutions/BinaryTreeLongestConsecutiveSequence.java)| O(n)|O(n) | Medium | Tree

|296|[Best Meeting Point](https://leetcode.com/problems/best-meeting-point/)|[Solution](../master/src/main/java/com/stevesun/solutions/BestMeetingPoint.java)| ?|? | Hard|

|295|[Find Median from Data Stream](https://leetcode.com/problems/find-median-from-data-stream/)|[Solution](../master/src/main/java/com/stevesun/solutions/FindMedianFromDataStream.java)| O(nlogn) | O(n) | Hard| Heap

|294|[Flip Game II](https://leetcode.com/problems/flip-game-ii/)|[Solution](../master/src/main/java/com/stevesun/solutions/FlipGameII.java)| ? | ?| Medium| Backtracking

|222|[Count Complete Tree Nodes](https://leetcode.com/problems/count-complete-tree-nodes/)|[Solution](../master/src/main/java/com/stevesun/solutions/CountCompleteTreeNodes.java)| O(?)|O(h) | Medium|

|220|[Contains Duplicate III](https://leetcode.com/problems/contains-duplicate-iii/)|[Solution](../master/src/main/java/com/stevesun/solutions/ContainsDuplicateIII.java)| O(nlogn)|O(n) | Medium| TreeSet

|219|[Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/)|[Solution](../master/src/main/java/com/stevesun/solutions/ContainsDuplicateII.java)| O(n)|O(n) | Easy| HashMap

|217|[Contains Duplicate](https://leetcode.com/problems/contains-duplicate/)|[Solution](../master/src/main/java/com/stevesun/solutions/ContainsDuplicate.java)| O(n)|O(n) | Easy| HashSet

|215|[Kth Largest Element in an Array](https://leetcode.com/problems/kth-largest-element-in-an-array/)|[Solution](../master/src/main/java/com/stevesun/solutions/_215.java)| O(nlogn)|O(n) | Medium| Heap

|212|[Word Search II](https://leetcode.com/problems/word-search-ii/)|[Solution](../master/src/main/java/com/stevesun/solutions/WordSearchII.java)| O(m*n*l)|O(l) | Hard | Trie

|190|[Reverse Bits](https://leetcode.com/problems/reverse-bits/)|[Solution](../master/src/main/java/com/stevesun/solutions/ReverseBits.java)| O(n)|O(1)| Easy | Bit Manipulation

|189|[Rotate Array](https://leetcode.com/problems/rotate-array/)|[Solution](../master/src/main/java/com/stevesun/solutions/_189.java)| O(n)|O(n), could be optimized to O(1) | Easy

|187|[Repeated DNA Sequences](https://leetcode.com/problems/repeated-dna-sequences/)|[Solution](../master/src/main/java/com/stevesun/solutions/_187.java)| O(n)|O(n) | Medium

|179|[Largest Number](https://leetcode.com/problems/largest-number/)|[Queue](../master/src/main/java/com/stevesun/solutions/BSTIterator_using_q.java) [Stack](../../blmaster/MEDIUM/src/medium/LargestNumber.java)| O(?) |O(?) | Medium|

|174|[Dungeon Game](https://leetcode.com/problems/dungeon-game/)|[Queue](../master/src/main/java/com/stevesun/solutions/BSTIterator_using_q.java) [Stack](../../blmaster/MEDIUM/src/medium/DungeonGame.java)| O(?) |O(?) | Hard|

|173|[Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/)|[Queue](../master/src/main/java/com/stevesun/solutions/BSTIterator_using_q.java) [Stack](../../blmaster/MEDIUM/src/medium/BSTIterator_using_stack.java)| O(1) |O(h) | Medium|

|157|[Read N Characters Given Read4](https://leetcode.com/problems/read-n-characters-given-read4/)|[Solution](../master/src/main/java/com/stevesun/solutions/ReadNCharactersGivenRead4.java)| O(n)|O(1) | Easy|

|156|[Binary Tree Upside Down](https://leetcode.com/problems/binary-tree-upside-down/)|[Solution](../master/src/main/java/com/stevesun/solutions/BinaryTreeUpsideDown.java)| O(n)|O(h) | Medium| Tree, Recursion

|155|[Min Stack](https://leetcode.com/problems/min-stack/)|[Solution](../master/src/main/java/com/stevesun/solutions/MinStack.java)| O(1)|O(n) | Easy| Stack

|152|[Maximum Product Subarray](https://leetcode.com/problems/maximum-product-subarray/)|[Solution](../master/src/main/java/com/stevesun/solutions/MaximumProductSubarray.java)| O(n)|O(1) | Medium| Array

|150|[Evaluate Reverse Polish Notation](https://leetcode.com/problems/evaluate-reverse-polish-notation/)|[Solution](../master/src/main/java/com/stevesun/solutions/EvaluateReversePolishNotation.java)| O(?)|O(?) | Medium

|149|[Max Points on a Line](https://leetcode.com/problems/max-points-on-a-line/)|[Solution](../master/src/main/java/com/stevesun/solutions/MaxPointsonaLine.java)| O(?)|O(?) | Hard|

|147|[Insertion Sort List](https://leetcode.com/problems/insertion-sort-list/)|[Solution](../master/src/main/java/com/stevesun/solutions/InsertionSortList.java) O(n^2)|O(1) | Medium| Linked List

|120|[Triangle](https://leetcode.com/problems/triangle/)|[Solution](../master/src/main/java/com/stevesun/solutions/Triangle.java)| O(m*n)|O(n) | Medium| DP

|119|[Pascal's Triangle II](https://leetcode.com/problems/pascals-triangle-ii/)|[Solution](../master/src/main/java/com/stevesun/solutions/PascalsTriangleII.java)| O(n^2)|O(1) | Easy|

|118|[Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)|[Solution](../master/src/main/java/com/stevesun/solutions/PascalsTriangle.java)| O(n^2)|O(1) | Easy|

|115|[Distinct Subsequences](https://leetcode.com/problems/distinct-subsequences/)|[Solution](../master/src/main/java/com/stevesun/solutions/DistinctSubsequences.java)| O(m*n)|O(m*n) | Hard| DP

|114|[Flatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)|[Solution](../master/src/main/java/com/stevesun/solutions/FlattenBinaryTreetoLinkedList.java)| O(n)|O(h) | Medium| Tree

|112|[Path Sum](https://leetcode.com/problems/path-sum/)|[Solution](../master/src/main/java/com/stevesun/solutions/PathSum.java)| O(n)|O(1) | Easy| DFS

|106|[Construct Binary Tree from Inorder and Postorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)|[Solution](../master/src/main/java/com/stevesun/solutions/_106.java)| O(n)|O(n) | Medium| Recursion, Tree

|105|[Construct Binary Tree from Preorder and Inorder Traversal](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)|[Solution](../master/src/main/java/com/stevesun/solutions/_105.java)| O(n)|O(n) | Medium| Recursion, Tree

|104|[Maximum Depth of Binary Tree](https://leetcode.com/problems/maximum-depth-of-binary-tree/)|[Solution](../master/src/main/java/com/stevesun/solutions/MaximumDepthOfBinaryTree.java)| O(n)|O(h) | Easy| DFS

|102|[Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/)|[Solution](../master/src/main/java/com/stevesun/solutions/BinaryTreeLevelOrderTraversal.java)| O(n)|O(h) | Easy| BFS

|99|[Recover Binary Search Tree](https://leetcode.com/problems/recover-binary-search-tree/)|[Solution](../master/src/main/java/com/stevesun/solutions/RecoverBinarySearchTree.java) | O(?) | O(?) | Hard |

|98|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)|[Solution](../master/src/main/java/com/stevesun/solutions/ValidateBinarySearchTree.java) | O(n) | O(h) | Medium | DFS/Recursion

|79|[Word Search](https://leetcode.com/problems/word-search/)|[Solution](../master/src/main/java/com/stevesun/solutions/WordSearch.java)|O(m*n*l) ? |O(m*n)|Medium|Backtracking/DFS

|78|[Subsets](https://leetcode.com/problems/subsets/)|[Solution](../master/src/main/java/com/stevesun/solutions/Subsets.java)|O(n^2) ? |O(1)|Medium|Backtracking

|76|[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)|[Solution](../master/src/main/java/com/stevesun/solutions/MinimumWindowSubstring.java)|O(n)|O(k)|Hard|Two Pointers

|74|[Search a 2D Matrix](https://leetcode.com/problems/search-a-2d-matrix/)|[Solution](../master/src/main/java/com/stevesun/solutions/Searcha2DMatrix.java)|O(logn)|O(1)|Medium| Binary Search

|72|[Edit Distance](https://leetcode.com/problems/edit-distance/)|[Solution](../master/src/main/java/com/stevesun/solutions/EditDistance.java)|O(m*n)|O(m+n)|Hard|

|71|[Simplify Path](https://leetcode.com/problems/simplify-path/)|[Solution](../master/src/main/java/com/stevesun/solutions/SimplifyPath.java)|O(n)|O(n)|Medium| Stack

|70|[Climbing Stairs](https://leetcode.com/problems/climbing-stairs/)|[Solution](../master/src/main/java/com/stevesun/solutions/ClimbingStairs.java)|O(n)|O(n)|Easy| DP

|56|[Merge Intervals](https://leetcode.com/problems/merge-intervals/)|[Solution](../master/src/main/java/com/stevesun/solutions/MergeIntervals.java)|O(n*logn)|O(1)|Hard|

|55|[Jump Game](https://leetcode.com/problems/jump-game/)|[Solution](../master/src/main/java/com/stevesun/solutions/JumpGame.java)|O(n)|O(1)|Medium|

|54|[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/)|[Solution](../master/src/main/java/com/stevesun/solutions/_54.java)|O(m*n)|O(m*n)|Medium| Array

|50|[Pow(x, n)](https://leetcode.com/problems/powx-n/)|[Solution](../master/src/main/java/com/stevesun/solutions/PowXN.java)|O(logn)|O(logn)|Medium|

|48|[Rotate Image](https://leetcode.com/problems/rotate-image/)|[Solution](../master/src/main/java/com/stevesun/solutions/_48.java)|O(n^2)|O(1)|Medium|Array

|47|[Permutations II](https://leetcode.com/problems/permutations-ii/)|[Solution](../master/src/main/java/com/stevesun/solutions/PermutationsII.java)|O(n*n!)|O(n)|Medium|Backtracking

/**The idea is very straightforward: