feat: add Solution.cpp for 0089.Gray Code

Author: Stackingrule

solution/0000-0099/0089.Gray Code/Solution.cpp

@@ -0,0 +1,10 @@
+class Solution {
+public:
+    vector<int> grayCode(int n) {
+        vector<int> res;
+        for (int i = 0; i < (1 << n); ++i) {
+        	res.push_back((i >> 1) ^ i);
+        }
+        return res;
+    }
+};