class Solution {
    List<List<Integer>> res = new ArrayList<>();
    LinkedList<Integer> path = new LinkedList<>();
    
    public List<List<Integer>> findSubsequences(int[] nums) {
        backTrack(nums,0);
        return res;
    }

    void backTrack(int[] nums,int index) {
        if (path.size() > 1) {
            res.add(new ArrayList<>(path));
        }
        
        HashMap<Integer,Integer> map = new HashMap<>();
        for (int i = index; i < nums.length; i++) {
            if ( !path.isEmpty() && nums[i] < path.getLast()) {
                continue;
            }
            if (map.getOrDefault(nums[i],0) >= 1) {
                continue;
            }
            path.add(nums[i]);
            map.put(nums[i], map.getOrDefault(nums[i],0)+1);
            backTrack(nums,i+1);
            path.removeLast();
        }
    }
}

class Solution {
    List<List<Integer>> res = new ArrayList<>();
    LinkedList<Integer> path = new LinkedList<>();
    boolean[] used;

    public List<List<Integer>> permute(int[] nums) {
        used = new boolean[nums.length];
        backTrack(nums);
        return res;
    }

    void backTrack(int[] nums) {
        if (path.size() == nums.length) {
            res.add(new ArrayList<>(path));
        }

        for (int i = 0; i < nums.length; i++) {
            if (used[i]) {
                continue;
            }
            path.add(nums[i]);
            used[i] = true;
            backTrack(nums);
            used[i] = false;
            path.removeLast();
        }
    }
}

class Solution {
    List<List<Integer>> res = new ArrayList<>();
    LinkedList<Integer> path = new LinkedList<>();
    boolean[] used;
    
    public List<List<Integer>> permuteUnique(int[] nums) {
        Arrays.sort(nums);
        used= new boolean[nums.length];
        backTrack(nums);
        return res;
    }

    void backTrack(int[] nums) {
        if (path.size() == nums.length) {
            res.add(new ArrayList<>(path));
            return;
        }

        for (int i = 0; i < nums.length; i++) {
            if (used[i]) {
                continue;
            }
            
            if (i > 0 && nums[i] == nums[i-1] && used[i-1]==false) {
            continue;
        }
            
            path.add(nums[i]);
            used[i] = true;
            backTrack(nums);
            path.removeLast();
            used[i] = false;
        }
    }
}