Java版本,涉及到stream流

class Solution {

    public static ArrayList<List<Integer>> res = new ArrayList();
    public List<List<Integer>> permutation(int[] nums) {
        Arrays.sort(nums);
        int[] ans = new int[nums.length];
        dfs(nums, 0, 0, 0, ans);
        return res;
    }

    public static void dfs(int[] nums, int u, int start, int state, int[] ans){
        if( u == nums.length) {
            List<Integer> list = Arrays.stream(ans).boxed().collect(Collectors.toList());
            res.add(list);
            return;
        }
        for(int i = start; i < nums.length; i ++){
            if((state >> i & 1) == 0 ){
                ans[i] = nums[u];
                if(u + 1 < nums.length && nums[u] == nums[u + 1]) dfs(nums, u + 1, i + 1, state + (1 << i), ans);
                else dfs(nums, u + 1,  0, state + (1 << i), ans);
            }
        }
    }
}