solves gray code

Author: anishLearnsToCode

README.md

@@ -79,6 +79,7 @@
 |  83  | [Remove Duplicates from Sorted List](https://leetcode.com/problems/remove-duplicates-from-sorted-list)                                                    |                   [![Java](assets/java.png)](src/RemoveDuplicatesFromSortedList.java) [![Python](assets/python.png)](python/remove_duplicates_from_linked_list.py)                   |                                                                                                                                   |
 |  86  | [Partition List](https://leetcode.com/problems/partition-list)                                                                                            |                                                                  [![Java](assets/java.png)](src/PartitionList.java)                                                                  |                                                                                                                                   |
 |  88  | [Merge Sorted Array](https://leetcode.com/problems/merge-sorted-array)                                                                                    |                                  [![Java](assets/java.png)](src/MergeSortedArray.java) [![Python](assets/python.png)](python/merge_sorted_array.py)                                  |                                                                                                                                   |
+|  89  | [Gray Code](https://leetcode.com/problems/gray-code)                                                                                                      |                                                                    [![Java](assets/java.png)](src/GrayCode.java)                                                                     |                                                                                                                                   |
 |  94  | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)                                                             |                       [![Java](assets/java.png)](src/BinaryTreeInorderTraversal.java) [![Python](assets/python.png)](python/binary_tree_inorder_traversal.py)                        |                                                                                                                                   |
 | 100  | [Same Tree](https://leetcode.com/problems/same-tree)                                                                                                      |                                          [![Java](assets/java.png)](src/SameTree.java) [![Python](assets/python.png)](python/same_tree.py)                                           |                                                                                                                                   |
 | 101  | [Symmetric Tree](https://leetcode.com/problems/symmetric-tree)                                                                                            |                                     [![Java](assets/java.png)](src/SymmetricTree.java) [![Python](assets/python.png)](python/symmetric_tree.py)                                      |                                                                                                                                   |

src/GrayCode.java

@@ -0,0 +1,19 @@
+// https://leetcode.com/problems/gray-code
+// T: O(2 ^ n)
+// S: O(2 ^ n)
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class GrayCode {
+    public List<Integer> grayCode(int n) {
+        final List<Integer> result = new ArrayList<>(1 << n);
+        result.add(0);
+        for (int i = 0, factor = 1 ; i < n ; i++, factor *= 2) {
+            for (int j = factor - 1 ; j >= 0 ; j--) {
+                result.add(result.get(j) + factor);
+            }
+        }
+        return result;
+    }
+}