78. Subsets

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:

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

Solution:

Method 1: DFS

Use DFS to traverse all possible combinations and store all of them into results.

To keep the subsets in order, we first sort the input array.



Code:

public class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        if (nums == null || nums.length == 0) {
            return result;
        }
        helper(nums, result, new ArrayList<Integer>(), 0);
        return result;
    }
    
    public void helper(int[] nums, List<List<Integer>> result, List<Integer> list, int pos) {
        result.add(new ArrayList<Integer>(list));
        
        for (int i = pos; i < nums.length; i++) {
            list.add(nums[i]);
            helper(nums, result, list, i + 1);
            list.remove(list.size() - 1);
        }
    }
}

Method 2: Bitset