Update README.md

Author: kamyu104

README.md

@@ -1,9 +1,9 @@
 LeetCode
 ======== 
 
-Up to date (2015-09-24), there are `269` Algorithms / `13` Database / `4` Shell questions on [LeetCode Online Judge](https://leetcode.com/).
+Up to date (2015-09-28), there are `270` Algorithms / `13` Database / `4` Shell questions on [LeetCode Online Judge](https://leetcode.com/).
 The number of questions is increasing recently.
-Here is the classification of all `286` questions.
+Here is the classification of all `287` questions.
 For more questions and solutions, you can see my [LintCode](https://github.com/kamyu104/LintCode) repository.
 I'll keep updating for full summary and better solutions. Stay tuned for updates.
 (Notes: "📖" means you need to subscribe to [LeetCode premium membership](https://leetcode.com/subscribe/) for the access to premium questions. )
@@ -332,6 +332,7 @@ 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)_ | Hard | 📖 |
 
 -- 
 ##Binary Search Tree