leetcode-Subsets

Given a set of distinct integers, nums, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• 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],  []
]
求一个数组的子集，要求每个子集内元素升序；
先将数组进行从小到大排序，再利用位运算枚举每种情况。
例如n个数字，有2^n个子集。即n个数字的组合情况，可用n个bits进行表示，bit位与数组是一一对应；
判断每个bit是否为1 进行枚举。
class Solution {public:    vector<vector <int> > subsets(vector<int>& nums) {        sort(nums.begin(),nums.end());        vector< vector<int> > ans;        int n = nums.size();        int i = 0,j= 0;        for(i = 0;i< 1 << n;i++)        {            vector<int> temp;            int index = 0;            int count = i;            while(count != 0)            {                if(count & 1 == 1)                {                    temp.push_back(nums[index]);                }                index++;                count = count >> 1;            }            ans.push_back(temp);        }           return ans;    }};