数组中相加为0的三元组

public ArrayList<ArrayList<Integer>> threeSum(int[] num) {
        ArrayList<ArrayList<Integer>> list = new ArrayList<>();
        if (num==null) return list;
        Arrays.sort(num);
        for (int i=0;i<num.length-2;i++){
            //固定第一个元素  去重
            if(i>0 && num[i]==num[i-1]) continue;
            ArrayList<ArrayList<Integer>> res = getList(i,num);
            list.addAll(res);
        }
        return list;
    }
    //转化为有序数组中找两个数等于目标数
    private ArrayList<ArrayList<Integer>> getList(int i, int[] num) {
        ArrayList<ArrayList<Integer>> res = new ArrayList<>();
        int target = 0-num[i];
        int left = i+1;
        int right = num.length-1;
        while (left<right){
            if (num[left]+num[right]>target){
                right--;
            }else if(num[left]+num[right]==target){
                //去重
                if(left>i+1 && num[left]==num[left-1]) {
                    left++;
                    continue;
                }
                ArrayList<Integer> list = new ArrayList<>();
                list.add(num[i]);
                list.add(num[left]);
                list.add(num[right]);
                res.add(list);
                left++;
            }else {
                left++;
            }
        }
        return res;
    }