LeetCode 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:

For example,[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

不重复集合求子集

每增加一个元素，都是在原来的子集基础上再添加该元素，即两倍原来的子集

public class Solution {
    public  ArrayList<ArrayList<Integer>> subsets(int[] S) {
        Arrays.sort(S);
        ArrayList<ArrayList<Integer>> result=new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> tmp=new ArrayList<Integer>();
        result.add(tmp);
        for(int i=0;i<S.length;i++)
        {
        	int len=result.size();
        	for(int j=0;j<len;j++)
        	{
        		tmp.clear();
        		tmp=(ArrayList<Integer>) result.get(j).clone(); //克隆是因为引用指向同一块内存
        		tmp.add(S[i]);
        		result.add((ArrayList<Integer>) tmp.clone());  //克隆不理解</span>
        	}
        }
        return result;
    }
}