From b63f9c514891f94298390716ecd5c853b5082ddd Mon Sep 17 00:00:00 2001
From: Qingfan Wu <wqfan555@gmail.com>
Date: Sat, 27 Apr 2019 15:52:26 -0700
Subject: [PATCH 1/2] [Math] Add a solution to Gary Code

---
 Math/GaryCode.swift | 18 ++++++++++++++++++
 README.md           |  6 +++---
 2 files changed, 21 insertions(+), 3 deletions(-)
 create mode 100644 Math/GaryCode.swift

diff --git a/Math/GaryCode.swift b/Math/GaryCode.swift
new file mode 100644
index 00000000..0397d0f4
--- /dev/null
+++ b/Math/GaryCode.swift
@@ -0,0 +1,18 @@
+/**
+ * Question Link: https://leetcode.com/problems/gray-code/
+ * Primary idea: the result of n can be derived from (n - 1) by reversing
+                 the order and prepending 1 to each number's binary representation
+ *
+ * Time Complexity: O(n), Space Complexity: O(2^n)
+ *
+ */
+
+class GaryCode {
+    func grayCode(_ n: Int) -> [Int] {
+        var codes = [0]
+        for i in 0..<n {
+            codes += codes.reversed().map { $0 | 1 << i }
+        }
+        return codes
+    }
+}
diff --git a/README.md b/README.md
index 999b4942..057d6445 100644
--- a/README.md
+++ b/README.md
@@ -83,7 +83,7 @@
 [Gas Station](https://leetcode.com/problems/gas-station/)| [Swift](./Array/GasStation.swift)| Medium| O(n)| O(1)|
 [Game of Life](https://leetcode.com/problems/game-of-life/)| [Swift](./Array/GameLife.swift)| Medium| O(n)| O(1)|
 [Task Scheduler](https://leetcode.com/problems/task-scheduler/)| [Swift](./Array/TaskScheduler.swift)| Medium| O(nlogn)| O(n)|
-[Sliding Window Maximum ](https://leetcode.com/problems/sliding-window-maximum/)| [Swift](./Array/SlidingWindowMaximum.swift)| Hard| O(n)| O(n)|	
+[Sliding Window Maximum ](https://leetcode.com/problems/sliding-window-maximum/)| [Swift](./Array/SlidingWindowMaximum.swift)| Hard| O(n)| O(n)|
 [Longest Consecutive Sequence](https://leetcode.com/problems/longest-consecutive-sequence/)| [Swift](./Array/LongestConsecutiveSequence.swift)| Hard| O(n)| O(n)|
 [Create Maximum Number](https://leetcode.com/problems/create-maximum-number/)| [Swift](./Array/CreateMaximumNumber.swift)| Hard| O(n^2)| O(n)|
 
@@ -745,9 +745,9 @@
 |	[Swift](./Stack/InorderTraversal.swift)	|	94	|	[Binary Tree Inorder Traversal](https://oj.leetcode.com/problems/binary-tree-inorder-traversal/)	| Medium	|
 |		|	93	|	[Restore IP Addresses](https://oj.leetcode.com/problems/restore-ip-addresses/)	| Medium	|
 |		|	92	|	[Reverse Linked List II](https://oj.leetcode.com/problems/reverse-linked-list-ii/)	| Medium	|
-|	(./DP/DecodeWays.swift)	|	91	|	[Decode Ways](https://oj.leetcode.com/problems/decode-ways/)	| Medium	|
+|	[Swift](./DP/DecodeWays.swift)	|	91	|	[Decode Ways](https://oj.leetcode.com/problems/decode-ways/)	| Medium	|
 |	[Swift](./DFS/SubsetsII.swift)	|	90	|	[Subsets II](https://oj.leetcode.com/problems/subsets-ii/)	| Medium	|
-|		|	89	|	[Gray Code](https://oj.leetcode.com/problems/gray-code/)	| Medium	|
+|	[Swift](./Math/GaryCode.swift)	|	89	|	[Gray Code](https://oj.leetcode.com/problems/gray-code/)	| Medium	|
 |	[Swift](./Sort/MergeSortedArray.swift) |	88	|	[Merge Sorted Array](https://oj.leetcode.com/problems/merge-sorted-array/)	| Easy	|
 |		|	87	|	[Scramble String](https://oj.leetcode.com/problems/scramble-string/)	| Hard	|
 |	[Swift](./LinkedList/PartitionList.swift)	|	86	|	[Partition List](https://oj.leetcode.com/problems/partition-list/)	| Medium	|

From a49ea387a5c30bb4e9fd62851e3f2868d892ebc4 Mon Sep 17 00:00:00 2001
From: Qingfan Wu <wqfan555@gmail.com>
Date: Sat, 4 May 2019 16:55:12 -0700
Subject: [PATCH 2/2] Update README.md

---
 README.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index 057d6445..c598607c 100644
--- a/README.md
+++ b/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 &hearts; 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 &hearts; 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 |