47. Permutations II

backtrack

 

 

 

class Solution {
    List<List<Integer>> res = new ArrayList<>();
    public List<List<Integer>> permuteUnique(int[] nums) {
        Arrays.sort(nums);
        backtrack(nums, new ArrayList<>(), new boolean[nums.length]);
        return res;
    }
    
    public void backtrack(int[] nums, List<Integer> list, boolean[] used) {
        if(list.size() == nums.length) {
            res.add(new ArrayList<>(list));
        }
        for(int i = 0; i < nums.length; i++) {
            if(used[i] || (i > 0 && nums[i-1] == nums[i] && !used[i-1])) continue;
            used[i] = true;
            list.add(nums[i]);
            backtrack(nums, list, used);
            list.remove(list.size() - 1);
            used[i] = false;
        }
    }   
}