Update 89-gray-code.js

Author: everthis

89-gray-code.js

@@ -1,3 +1,22 @@
+/**
+ * @param {number} n
+ * @return {number[]}
+ */
+const grayCode = function(n) {
+  if (n === 0) {
+    return [0]
+  }
+  const temp = grayCode(n - 1)
+  const nums = [].concat(temp)
+  const addNum = 1 << (n - 1)
+  for (let i = temp.length - 1; i >= 0; i--) {
+    nums.push(addNum + temp[i])
+  }
+  return nums
+}
+
+// another
+
 /**
  * @param {number} n
  * @return {number[]}