[LeetCode] Subsets II

Subsets II

Given a collection of integers that might contain duplicates, 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 = [1,2,2], a solution is:

[  [2],  [1],  [1,2,2],  [2,2],  [1,2],  []]

解题思路：

去重的话用一个set来记录。枚举的话，可以二进制递增来枚举。i从0递增到2^n-1，若i的二进制表示中，相应位为1，则添加到项中。

class Solution {public:    vector<vector<int>> subsetsWithDup(vector<int>& nums) {        vector<vector<int>> result;        set<vector<int>> contains;  //已经包含的        std::sort(nums.begin(), nums.end());                int num = 1 << nums.size();        for(int i=0; i<num; i++){            int flag = i;            int j=0;            vector<int> item;            while(flag!=0){                if(flag&0x1==1){                    item.push_back(nums[j]);                }                flag = flag>>1;                j++;            }            if(contains.find(item)==contains.end()){                contains.insert(item);                result.push_back(item);            }        }                        return result;    }};