Create gray-code.cpp

Author: kamyu104

C++/gray-code.cpp

@@ -0,0 +1,30 @@
+// Time:  (2^n)
+// Space: O(1)
+
+class Solution {
+public:
+    vector<int> grayCode(int n) {
+        vector<int> result = {0};
+        for (int i = 0; i < n; ++i) {
+            for (int j = result.size() - 1; j >= 0; --j) {
+                result.emplace_back(1 << i | result[j]);
+            }
+        }
+        return result;
+    }
+};
+
+// Time:  (2^n)
+// Space: O(1)
+// Proof of closed form formula could be found here:
+// http://math.stackexchange.com/questions/425894/proof-of-closed-form-formula-to-convert-a-binary-number-to-its-gray-code
+class Solution2 {
+public:
+    vector<int> grayCode(int n) {
+        vector<int> result;
+        for (int i = 0; i < 1 << n; ++i) {
+            result.emplace_back(i >> 1 ^ i);
+        }
+        return result;
+    }
+};