[LeetCode][JavaScript]Gray Code

Gray Code

The gray code is a binary numeral system where two successive values differ in only one bit.

Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0.

For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:

00 - 0
01 - 1
11 - 3
10 - 2

Note:
For a given n, a gray code sequence is not uniquely defined.

For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.

For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.

https://leetcode.com/problems/gray-code/

使用dfs得到符合题意的答案，但答案只接受格雷码的顺序，而且大数据用dfs会超时。

 1 /**
 2  * @param {number} n
 3  * @return {number[]}
 4  */
 5 var grayCode = function(n) {
 6     var len = Math.pow(2, n), res = [];
 7     for(var i = 0; i < len; i++)
 8         res.push(i ^ (i >> 1));
 9     return res;
10 }

DFS，顺序不对不能AC。

 1 /**
 2  * @param {number} n
 3  * @return {number[]}
 4  */
 5 var grayCode_WA = function(n) {
 6     if(n === 0) return [0];
 7     var i, map = [], visited = {}, len = Math.pow(2, n);
 8     for(i = 0; i < n; i++)
 9         map[i] = 0;
10     visited[map.join("")] = true;
11     return dfs(map, [0]);
12
13     function dfs(map, res){
14         if(res.length === len)
15             return res;
16         var key = "", tmp;
17         for(var i = 0; i < n; i++){
18             map[i] === 0 ? map[i] = 1 : map[i] = 0;
19             key = map.join("");
20             if(!visited[key]){
21                 visited[key] = true;
22                 res.push(parseInt(key, 2));
23                 tmp = dfs(map, res);
24                 if(tmp) return tmp;
25                 res.pop();
26                 visited[key] = false;
27             }
28             map[i] === 0 ? map[i] = 1 : map[i] = 0;
29         }
30         return false;
31     }
32 };