示例 1：
输入：nums = [-1,0,1,2,-1,-4]输出：[[-1,-1,2],[-1,0,1]]
来源：力扣（LeetCode）链接：https://leetcode-cn.com/problems/3sum著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

    public List<List<Integer>> threeSum(int[] nums) {        List<List<Integer>> result = new ArrayList<>();        Arrays.sort(nums);        for (int i = 0; i < nums.length - 2; i++) {            if (nums[i] > 0) break;            if (i > 0 && nums[i] == nums[i - 1]) continue;            int left = i + 1;            int right = nums.length - 1;            while (left < right) {                int sum = nums[i] + nums[left] + nums[right];                if (sum < 0) {                    while (left < right && nums[left] == nums[++left]) ;                } else if (sum > 0) {                    while (left < right && nums[right] == nums[--right]) ;                } else {                    result.add(new ArrayList<>(Arrays.asList(nums[i], nums[left], nums[right])));                    while (left < right && nums[left] == nums[++left]) ;                    while (left < right && nums[right] == nums[--right]) ;                }            }        }        return result;    }