78.子集

操作元素不重复

class Solution {
    List<List<Integer>> result = new ArrayList<>();
    LinkedList<Integer> path = new LinkedList<>();
    public List<List<Integer>> subsets(int[] nums) {
        helper(nums, 0);
        return result;
    }
    public void helper(int[] nums, int startIndex){
        result.add(new ArrayList<>(path));
        for(int i = startIndex; i < nums.length; i++){
            path.add(nums[i]);
            helper(nums, i + 1);
            path.removeLast();
        }
    }
}

90.子集II

操作元素可能包含重复元素

class Solution {
    List<List<Integer>> result = new ArrayList<>();
    LinkedList<Integer> path = new LinkedList<>();
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        Arrays.sort(nums);
        helper(nums, 0);
        return result;
    }
    public void helper(int[] nums, int startIndex){
        result.add(new ArrayList<>(path));
        for(int i = startIndex; i < nums.length; i++){
            //层级去重
            if(i > startIndex && nums[i - 1] == nums[i]) continue;
            path.add(nums[i]);
            helper(nums, i + 1);
            path.removeLast();
        }
    }
}