lc90回溯

class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        Arrays.sort(nums);
        List<List<Integer>> res=new ArrayList<>();
        boolean[] visit=new boolean[nums.length];
        bs(res,new ArrayList<Integer>(),nums,0,visit);
        return res;

    }
     private void bs(List<List<Integer>> res,List<Integer> tmp,int[] nums,int start,boolean[] visit){
        res.add(new ArrayList<>(tmp));
        for(int i=start;i<nums.length;i++){
            if(i!=0&&nums[i]==nums[i-1]&&!visit[i-1]){
                continue;
            }
            tmp.add(nums[i]);
            visit[i]=true;
            bs(res,tmp,nums,i+1,visit);
            tmp.remove(tmp.size()-1); 
            visit[i]=false; 
            }
    }

}