17题 Subsets

Subsets

Description
Given a set with distinct integers, return all possible subsets.

public class Solution {
    /**
     * @param nums: A set of numbers
     * @return: A list of lists
     */
    public List<List<Integer>> subsets(int[] nums) {
        // write your code here
        if(nums == null){
            return null ;
        }
        List<List<Integer>> results = new ArrayList<>() ;
        helper(nums , results , new ArrayList<Integer>() , 0) ;
        return results ;

    }
    public void helper(int[] nums , List<List<Integer>> results , List<Integer> subset , int startIndex){
        results.add(new ArrayList<Integer>(subset)) ;
        for(int i = startIndex ; i < nums.length ; i++){
            subset.add(nums[i]) ;
            helper(nums , results , subset , i+1);
            subset.remove(subset.size()-1);
        }
    }
}