【LeetCode】Subsets (2 solutions)

Subsets

Given a set of distinct integers, S, 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 S = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

参照Subsets II的解法

解法一：

class Solution {
public:
    vector<vector<int> > subsets(vector<int> &S) {
        vector<vector<int> > result;
        int size = S.size();
        for(int i = 0; i < pow(2.0, size); i ++)
        {//2^size subsets
            vector<int> cur;
            int tag = i;
            for(int j = size-1; j >= 0; j --)
            {//for each subset, the binary presentation has size digits
                if(tag%2 == 1)
                    cur.push_back(S[j]);
                tag >>= 1;
                if(!tag)
                    break;
            }
            sort(cur.begin(), cur.end());
            result.push_back(cur);
        }
        return result;
    }
};

解法二：

class Solution {
public:
    vector<vector<int> > subsets(vector<int> &S) {
        vector<vector<int> > result;
        vector<int> cur;
        result.push_back(cur);  //empty set
        sort(S.begin(), S.end());
        for(int i = 0; i < S.size(); i ++)
        {
            int exist = result.size();
            for(int j = 0; j < exist; j ++)
            {
                cur = result[j];
                cur.push_back(S[i]);
                result.push_back(cur);
            }
        }
        return result;
    }
};