Update README.md

Author: kamyu104

README.md

@@ -278,6 +278,7 @@ Shell
 167| [Two Sum II - Input array is sorted](https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/) | [Python](./Python/two-sum-ii-input-array-is-sorted.py) | _O(n)_ | _O(1)_ | Medium | 📖 |
 259 | [3Sum Smaller](https://leetcode.com/problems/3sum-smaller/) | [C++](./C++/3sum-smaller.cpp) [Python](./Python/3sum-smaller.py) | _O(n^2)_ | _O(1)_ | Medium | 📖, LintCode |
 283 | [Move Zeros](https://leetcode.com/problems/move-zeros/) | [C++](./C++/move-zeros.cpp) [Python](./Python/move-zeros.py) | _O(n)_ | _O(1)_ | Easy | |
+287| [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)| [C++](./C++/find-the-duplicate-number.cpp) [Python](./Python/find-the-duplicate-number.py) | _O(n)_ | _O(1)_ | Medium | 📖 | Binary Search, Two Pointers |
 
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@@ -332,7 +333,6 @@ Shell
 222| [Count Complete Tree Nodes](https://leetcode.com/problems/count-complete-tree-nodes/) | [C++](./C++/count-complete-tree-nodes.cpp) [Python](./Python/count-complete-tree-nodes.py) | _O((logn)^2)_ | _O(1)_ | Medium ||
 275| [H-Index II](https://leetcode.com/problems/h-index-ii/) | [C++](./C++/h-index-ii.cpp) [Python](./Python/h-index-ii.py) | _O(logn)_ | _O(1)_ | Medium || Binary Search |
 278| [First Bad Version](https://leetcode.com/problems/first-bad-version/) | [C++](./C++/first-bad-version.cpp) [Python](./Python/first-bad-version.py) | _O(logn)_ | _O(1)_ | Easy | LintCode ||
-287| [Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)| [C++](./C++/find-the-duplicate-number.cpp) [Python](./Python/find-the-duplicate-number.py) | _O(nlogn)_ | _O(1)_ | Medium | 📖 |
 
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 ##Binary Search Tree