Update README.md

Author: wqfan

README.md

@@ -4,7 +4,7 @@
 ![Leetcode](./logo.png?style=centerme)
 
 ## Progress
-[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 272 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them.
+[Problem Status](#problem-status) shows the latest progress to all 800+ questions. Currently we have 273 completed solutions. Note: questions with ♥ mark means that you have to **Subscript to premium membership** of LeetCode to unlock them.
 
 ## Contributors
 
@@ -304,6 +304,7 @@
 [Container With Most Water](https://leetcode.com/problems/container-with-most-water/)| [Swift](./Math/ContainerMostWater.swift)| Medium| O(n)| O(1)|
 [Counting Bits](https://leetcode.com/problems/counting-bits/)| [Swift](./Math/CountingBits.swift)| Medium| O(n)| O(n)|
 [K-th Smallest in Lexicographical Order](https://leetcode.com/problems/k-th-smallest-in-lexicographical-order/)| [Swift](./Math/KthSmallestLexicographicalOrder.swift)| Hard| O(n)| O(1)|
+[Gary Code](https://leetcode.com/problems/gray-code/)| [Swift](./Math/GaryCode.swift)| Medium| O(n)| O(2^n)|
 
 ## Search
 | Title | Solution | Difficulty | Time | Space |