public List<List<Integer>> subsets(int[] nums) {

List<List<Integer>> ans = new ArrayList<>();

if(nums.length==0){

return ans;

}

ans.add(new ArrayList<>());

helper(nums, ans, new ArrayList<>(),0);

return ans;

}

private void helper(int[] nums, List<List<Integer>> ans, List<Integer> curList, int index){

if(index>=nums.length){

return;

} else{

for(int i=index;i<nums.length;i++){

curList.add(nums[i]);

ans.add(new ArrayList<>(curList));

helper(nums, ans, curList, i+1);

curList.remove(curList.size()-1);

}

}

}

public List<List<Integer>> subsets(int[] nums) {

List<List<Integer>> result = new ArrayList<>();

if(nums == null || nums.length == 0)

return result;

generateSubSets(nums, nums.length, 0, new ArrayList<>(), result);

return result;

}

private static void generateSubSets(int nums[], int n, int index, List<Integer> temp,

List<List<Integer>> result){

result.add(new ArrayList<>(temp));

for(int i=index;i<n;i++){

temp.add(nums[i]);

generateSubSets(nums, n, i + 1, temp, result);

temp.remove(temp.size() - 1);

}

}