subsets2.java

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

        List<Integer> subset = new ArrayList<Integer>();
        helper(nums, 0, subset, results);
        
        return results;
        
        
    }
    public void helper(int[] nums, int startIndex, List<Integer> subset, List<List<Integer>> results){
        results.add(new ArrayList<Integer>(subset));
        for(int i=startIndex; i<nums.length; i++){
            if (i != startIndex && nums[i]==nums[i-1]) {
                continue;
            }
            subset.add(nums[i]);
            helper(nums, i+1, subset, results);
            subset.remove(subset.size()-1);
        }
    }
}

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

        ArrayList<Integer> subset = new ArrayList<>();
        helper(nums, 0, subset, results);
        
         return results;
        
        
    }
    public void helper(int[] nums, int startIndex, List<Integer> subset, List<List<Integer>> results){
        results.add(new ArrayList<Integer>(subset));
        for(int i=startIndex; i<nums.length; i++){
            if (i != startIndex && nums[i]==nums[i-1]) {
                continue;
            }
            subset.add(nums[i]);
            helper(nums, i+1, subset, results);
            subset.remove(subset.size()-1);
        }
    }
}