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69 | 69 | |249|[Group Shifted Strings](https://leetcode.com/problems/group-shifted-strings/)|[Solution](../../blob/master/EASY/src/easy/GroupShiftedStrings.java)| O(nlogn)| O(n)| |
70 | 70 | |246|[Strobogrammatic Number](https://leetcode.com/problems/strobogrammatic-number/)|[Solution](../../blob/master/EASY/src/easy/StrobogrammaticNumber.java)| O(n)| O(1)| |
71 | 71 | |243|[Shortest Word Distance](https://leetcode.com/problems/shortest-word-distance/)|[Solution](../../blob/master/EASY/src/easy/ShortestWordDistance.java)| O(n)| O(1)| |
| 72 | +|226|[Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)|[Solution](../../blob/master/EASY/src/easy/InvertBinaryTree.java)| O(n)|O(h) | Easy| DFS, recursion |
72 | 73 | |223|[Rectangle Area](https://leetcode.com/problems/rectangle-area/)|[Solution](../../blob/master/EASY/src/easy/RectangleArea.java)| O(1)|O(1)| Easy| |
73 | 74 | |219|[Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/)|[Solution](../../blob/master/EASY/src/easy/ContainsDuplicateII.java)| O(n)|O(n) | Easy| HashMap |
74 | 75 | |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| |
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