题目：
Given a set of distinct integers, nums, return all possible subsets.
Note: The solution set must not contain duplicate subsets.
For example,If nums = [1,2,3], a solution is:
[
[3],
[1],
[2],
[1,2,3],
[1,3],
[2,3],
[1,2],
[]
]
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题目大意，就是找出一个数组中的所有子集。
解答：参照leetcode中的讨论
屏幕快照 2016-12-05 下午8.00.58.png
1代表会取到nums中的对应的值，0代表没有。
代码：
/**
* @param {number[]} nums
* @return {number[][]}
*/
var subsets = function(nums) {
if (nums.length === 0)
return [];
var len = nums.length,
count = Math.pow(2, len),
result = [];
for (var i = 0; i < count; i++) {
// to binary string
var str = i.toString(2);
// get one subset from binary string
var subset = [];
// iterate the string from back to front since our binary string is
// e.g.: "11" instead of "011" when i = 3
for (var k = str.length - 1; k >= 0; k--) {
if (str[k] == '1')
subset.unshift(nums[len - str.length + k]);
}
result.push(subset);
}
return result;
};
