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 public ArrayList<ArrayList<Integer>> threeSum (int[] num) {
        ArrayList<ArrayList<Integer>> ans = new ArrayList<ArrayList<Integer>>();
        Arrays.sort(num);

        for(int i=0;i<num.length && num[i]<=0;i++){
            if(i>0&&num[i]==num[i-1]){
                continue;
            }
            int j=i+1,k=num.length-1;
            while (j<k) {
                int valuei=num[i];
                int valuej=num[j];
                int valuek=num[k];
                int sum = valuei+valuej+valuek;
                if(sum==0){
                    ans.add(new ArrayList<>(Arrays.asList(valuei,valuej,valuek)));
                }
                if(sum>0){
                    while (j<k&&num[k]==valuek) {
                        k--;
                    }
                }else{
                    while (j<k&&num[j]==valuej) {
                        j++;
                    }
                }
            }
        }
        return ans;
    }