add: 只出现一次的数字等

src/array/gray-code.js

@@ -0,0 +1,24 @@
+// LeetCode 89. 格雷编码 https://leetcode-cn.com/problems/gray-code/
+// LintCode 411. 格雷编码 https://www.lintcode.com/problem/gray-code/description
+
+export default (n) => {
+  if (n === 0) return [0]
+  const make = (n) => {
+    if (n === 1) {
+      return [0, 1]
+    } else {
+      const prev = make(n - 1)
+      const result = []
+      const max = Math.pow(2, n) - 1
+      for (let i = 0, len = prev.length; i < len; i++) {
+        result[i] = `0${prev[i]}`
+        result[max - i] = `1${prev[i]}`
+      }
+      return result
+    }
+  }
+
+  return make(n).map(val => {
+    return parseInt(val, 2)
+  })
+}