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;
}
};