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3 | 3 | |-----|--------------------------|---------------------|-------|--------|------------|-----|------ |
4 | 4 | |350|[Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/)|[Solution](../../blob/master/EASY/src/easy/IntersectionOfTwoArraysII.java)| O(m+n)|O((m+n)) could be optimized | Easy| HashMap, Binary Search |
5 | 5 | |349|[Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/)|[Solution](../../blob/master/EASY/src/easy/IntersectionOfTwoArrays.java)| O(m+n)|O(min(m,n)) | Easy| Two Pointers, Binary Search |
| 6 | +|325|[Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/)|[Solution] | O(n)|O(n) | Medium| HashMap |
| 7 | +|314|[Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/)|[Solution](../../blob/master/MEDIUM/src/medium/BinaryTreeVerticalOrderTraversal.java)| O(n)|O(n) | Medium| HashMap, BFS |
6 | 8 | |301|[Remove Invalid Parentheses](https://leetcode.com/problems/remove-invalid-parentheses/)|[Solution]| ? | ? | Hard| BFS |
7 | 9 | |283|[Move Zeroes](https://leetcode.com/problems/move-zeroes/)|[Solution](../../blob/master/EASY/src/easy/MoveZeroes.java)| O(n)|O(1) | Easy| |
8 | 10 | |278|[First Bad Version](https://leetcode.com/problems/first-bad-version/)|[Solution](../../blob/master/EASY/src/easy/FirstBadVersion.java)| O(logn)|O(1) | Easy| Binary Search |
| 11 | +|273|[Integer to English Words](https://leetcode.com/problems/integer-to-english-words/)|[Solution]| |
| 12 | +|257|[Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)|[Solution](../../blob/master/EASY/src/easy/BinaryTreePaths.java) | O(n*h) | O(h) | DFS/Recursion |
9 | 13 | |209|[Minimum Size Subarray Sum](https://leetcode.com/problems/minimum-size-subarray-sum/)|[Solution](../../blob/master/MEDIUM/src/medium/MinimumSizeSubarraySum.java)| O(n)|O(1) | Medium| |
| 14 | +|206|[Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/)|[Solution](../../blob/master/EASY/src/easy/ReverseLinkedList.java)| O(n)|O(1) | Easy |
10 | 15 | |200|[Number of Islands](https://leetcode.com/problems/number-of-islands/)|[Union Find](../../blob/master/MEDIUM/src/medium/NumberOfIslandsUnionFind.java) [DFS](../../blob/master/MEDIUM/src/medium/NumberofIslandsDFS.java)| O(m*n)|O(m*n) | Medium| Union Find, DFS |
| 16 | +|173|[Binary Search Tree Iterator](https://leetcode.com/problems/binary-search-tree-iterator/)|[Queue](../../blob/master/MEDIUM/src/medium/BSTIterator_using_q.java) [Stack](../../blob/master/MEDIUM/src/medium/BSTIterator_using_stack.java)| O(1) |O(h) | Medium| |
11 | 17 | |140|[Word Break II](https://leetcode.com/problems/word-break-ii/)|[Solution](../../blob/master/HARD/src/hard/WordBreakII.java)| ? |O(n^2) | Hard| Backtracking/DFS |
12 | 18 | |139|[Word Break](https://leetcode.com/problems/word-break/)|[Solution](../../blob/master/MEDIUM/src/medium/WordBreak.java)| O(n^2)|O(n) | Medium| DP |
13 | 19 | |133|[Clone Graph](https://leetcode.com/problems/clone-graph/)|[Solution](../../blob/master/MEDIUM/src/medium/CloneGraph.java)| O(n)|O(n) | Medium| HashMap, BFS |
| 20 | +|125|[Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)|[Solution](../../blob/master/EASY/src/easy/ValidPalindrome.java)| O(n)|O(1) | Easy| Two Pointers |
| 21 | +|122|[Best Time to Buy and Sell Stock II](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/)|[Solution](../../blob/master/MEDIUM/src/medium/BestTimeToBuyAndSellStockII.java)| O(n)|O(1) | Medium | Greedy |
| 22 | +|121|[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)|[Solution](../../blob/master/EASY/src/easy/BestTimeToBuyAndSellStock.java)| O(n)|O(1) | Easy| DP |
14 | 23 | |117|[Populating Next Right Pointers in Each Node II](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/)|[Solution](../../blob/master/HARD/src/hard/PopulatingNextRightPointersinEachNodeII.java)| O(n)|O(1) | Hard| BFS |
15 | 24 | |116|[Populating Next Right Pointers in Each Node](https://leetcode.com/problems/populating-next-right-pointers-in-each-node/)|[Solution](../../blob/master/MEDIUM/src/medium/PopulatingNextRightPointersinEachNode.java)| O(n)|O(1) | Medium| BFS |
16 | 25 | |91|[Decode Ways](https://leetcode.com/problems/decode-ways/)|[Solution](../../blob/master/MEDIUM/src/medium/DecodeWays.java)| O(n)|O(n) | Medium| DP |
| 26 | +|98|[Validate Binary Search Tree](https://leetcode.com/problems/validate-binary-search-tree/)|[Solution] | O(n) | O(1) | Medium | DFS/Recursion |
| 27 | +|79|[Word Search](https://leetcode.com/problems/word-search/)|[Solution](../../blob/master/MEDIUM/src/medium/WordSearch.java)|O(m*n*l) ? |O(m*n)|Medium|Backtracking/DFS |
| 28 | +|78|[Subsets](https://leetcode.com/problems/subsets/)|[Solution](../../blob/master/MEDIUM/src/medium/Subsets.java)|O(n^2) ? |O(1)|Medium|Backtracking |
17 | 29 | |76|[Minimum Window Substring](https://leetcode.com/problems/minimum-window-substring/)|[Solution](../../blob/master/HARD/src/hard/MinimumWindowSubstring.java)|O(n)|O(k)|Hard|Two Pointers |
| 30 | +|75|[Sort Colors](https://leetcode.com/problems/sort-colors/)|[Solution]|O(n)|O(1)|Medium |
18 | 31 | |67|[Add Binary](https://leetcode.com/problems/add-binary/)|[Solution](../../blob/master/EASY/src/easy/AddBinary.java)|O(n)|O(1)|Easy| |
19 | 32 | |56|[Merge Intervals](https://leetcode.com/problems/merge-intervals/)|[Solution](../../blob/master/HARD/src/hard/MergeIntervals.java)|O(n*logn)|O(1)|Hard| |
| 33 | +|43|[Multiply Strings](https://leetcode.com/problems/multiply-strings/)|[Solution]|||Medium |
20 | 34 | |23|[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)|[Solution](../../blob/master/HARD/src/hard/MergeKSortedList.java)|O(n*logk)|O(logk)|Hard|Heap |
21 | 35 | |17|[Letter Combinations of a Phone Number](https://leetcode.com/problems/letter-combinations-of-a-phone-number/)|[Solution](../../blob/master/MEDIUM/src/medium/LetterCombinationsofaPhoneNumber.java)|O(n*4^n)|O(n)|Medium|Backtracking |
22 | 36 | |15|[3Sum](https://leetcode.com/problems/3sum/)|[Solution](../../blob/master/MEDIUM/src/medium/_3Sum.java)|O(nlogn)|O(1)|Medium|Two Pointers |
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