代码，思路和yxc视频中讲的一样，只是因为Java引用调用的问题，挖坑的手法不一样

class Solution {
    List<List<Integer>> ans = new ArrayList<>();
    public List<List<Integer>> permutation(int[] nums) {
        Arrays.sort(nums);
        dfs(nums, 0, 0, 0, new int[nums.length]);
        return ans;
    }
    public void dfs(int[] nums, int n, int start, int state, int[] path){
        if(n == nums.length) {
            List<Integer> t = new ArrayList<>();
            for(int i:path){
                t.add(i);
            }
            ans.add(t);
            return;
        }
        if(n == 0 || nums[n] != nums[n - 1]) start = 0;
        for(int i = start; i < nums.length; i++){
            if( ((state >> i) & 1) == 0){
                path[i] = nums[n];
                dfs(nums, n + 1, i + 1, state + (1 << i), path);
            }
        }
    }
}