Given a set of distinct integers, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example,
If nums = [1,2,3], a solution is:

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

Backtracking solution

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public class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> list = new ArrayList<>();
        Arrays.sort(nums);
        backtrack(list, new ArrayList<>(), nums, 0);
        return list;
    }
    
    private void backtrack(List<List<Integer>> list , List<Integer> tempList, int [] nums, int start){
        list.add(new ArrayList<>(tempList));
        for(int i = start; i < nums.length; i++){
            tempList.add(nums[i]);
            backtrack(list, tempList, nums, i + 1);
            tempList.remove(tempList.size() - 1);
        }
    }
}

Bit solution

code and explanation here

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public List<List<Integer>> subsets(int[] S) {
	Arrays.sort(S);
	int totalNumber = 1 << S.length;
	List<List<Integer>> collection = new ArrayList<List<Integer>>(totalNumber);
	for (int i=0; i<totalNumber; i++) {
		List<Integer> set = new LinkedList<Integer>();
		for (int j=0; j<S.length; j++) {
			if ((i & (1<<j)) != 0) {
				set.add(S[j]);
			}
		}
		collection.add(set);
	}
	return collection;
}