[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/

---

直接用格雷码转换的公式，右移一位与自身异或。

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。

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

DFS，顺序不对不能AC。

/**
 * @param {number} n
 * @return {number[]}
 */
var grayCode_WA = function(n) {
    if(n === 0) return [0];
    var i, map = [], visited = {}, len = Math.pow(2, n);
    for(i = 0; i < n; i++)
        map[i] = 0;
    visited[map.join("")] = true;
    return dfs(map, [0]);

    function dfs(map, res){
        if(res.length === len)
            return res;
        var key = "", tmp;
        for(var i = 0; i < n; i++){
            map[i] === 0 ? map[i] = 1 : map[i] = 0;
            key = map.join("");
            if(!visited[key]){
                visited[key] = true;
                res.push(parseInt(key, 2));
                tmp = dfs(map, res);
                if(tmp) return tmp;
                res.pop();
                visited[key] = false;
            }
            map[i] === 0 ? map[i] = 1 : map[i] = 0;
        }
        return false;
    }
};