java HashSet straightforward
\nclass Solution {\n    public List<List<Integer>> findDifference(int[] nums1, int[] nums2) {\n        Set<Integer> s1 = new HashSet<Integer>();\n        Set<In
```\nclass Solution {\n    public List<List<Integer>> findDifference(int[] nums1, int[] nums2) {\n        Set<Integer> s1 = new HashSet<Integer>();\n        Set<Integer> s2 = new HashSet<Integer>();\n        \n        for(int i : nums1){\n            s1.add(i);\n        }\n        for(int i : nums2){\n            s2.add(i);\n        }\n        List<List<Integer>> ret = new ArrayList();\n        ret.add(new ArrayList());\n        ret.add(new ArrayList());\n        for(int i : s1){\n            if(!s2.contains(i)){\n                ret.get(0).add(i);\n            }\n        }\n        for(int i : s2){\n            if(!s1.contains(i)){\n                ret.get(1).add(i);\n            }\n        }\n        \n        return ret;\n    }\n}\n```
['Java']