LeetCode之Subsets

//递归解法
class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int> > res;
        if(nums.empty()) return res;
        sort(nums.begin(), nums.end());
        
        for(int count = 0; count < nums.size()+1; ++count){
            vector<int> tmp;
            subsets_sub(nums, res, tmp, 0, count);
        }
        return res;
    }
    
    void subsets_sub(const vector<int> &nums, vector<vector<int> > &res,
		vector<int> &tmp_res, int start, int count){
        /*函数功能：递归获取包含count个数的子数组。*/
		if(count == 0){
			res.push_back(tmp_res);
			return;
		}
        for(int i = start; i < nums.size(); ++i){
            if(count <= nums.size()-i){
                tmp_res.push_back(nums[i]);
                subsets_sub(nums, res, tmp_res, i+1, count-1);
                tmp_res.pop_back();
            }
        }
    }
};

//迭代解法
class Solution {
public:
    vector<vector<int>> subsets(vector<int>& nums) {
        vector<vector<int> > res;
        if(nums.empty()) return res;
        sort(nums.begin(), nums.end());

		res.push_back(vector<int>());
		for(int i = 0; i < nums.size(); ++i){
			res.reserve(res.size()*2);
			int half = res.size();
			for(int j = 0; j < half; ++j){
				res.push_back(res[j]);
				res[half+j].push_back(nums[i]);
			}

		}
		return res;
    }
};