[LeetCode104]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],
  []
]

Analysis:

DFS

这个就是排列组合中的排列问题。递归如下逻辑：
Func Generate
对于输入字符串s的每一位字符
选取该字符到子集合中，并输出
如果，当前字符不是最后一位字符
递归调用Generate,处理下一位字符

Java

public class Solution {
    List<List<Integer>> result;
	List<Integer> solu;
	public List<List<Integer>> subsets(int[] S) {
        result = new ArrayList<>();
        solu = new ArrayList<>();
        Arrays.sort(S);
        getSubset(S, 0);
        return result;
    }
	public void getSubset(int []S, int st){
		if(solu.size()<=S.length){
			result.add(new ArrayList<>(solu));
		}
		for(int i=st; i<S.length;i++){
			solu.add(S[i]);
			getSubset(S, i+1);
			solu.remove(solu.size()-1);
		}
	}
}

C++

class Solution {
public:
    void genSet(vector<int> &S, vector<vector<int>> &result, vector<int> &solution,int level){
        for(int i=level; i<S.size(); i++){
            solution.push_back(S[i]);
            result.push_back(solution);
            if(i<S.size()-1){
                genSet(S,result,solution,i+1);
            }
            solution.pop_back();
            }
    }
    vector<vector<int> > subsets(vector<int> &S) {
        vector<vector<int>> result;
        vector<int> solution;
        if(S.size() == 0) return result;
        result.push_back(solution);
        sort(S.begin(), S.end());
        
        genSet(S,result, solution,0);
        return result;
        }
};