LeetCode15 3Sum

题目：

       Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

       Note:

       The solution set must not contain duplicate triplets.

       Example:

       Given array nums = [-1, 0, 1, 2, -1, -4],

       A solution set is:

       [

         [-1, 0, 1],

         [-1, -1, 2] 

       ]

public class TribleSum {
    public static List<List<Integer>> threeSum(int[] nums) {
        if (nums == null || nums.length < 3)
            return null;
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            int left = i + 1;
            int right = nums.length - 1;
            int x = nums[i];
            while (left < right) {
                if ((x + nums[left] + nums[right]) == 0) {

                    res.add(Arrays.asList(x, nums[left], nums[right]));
                    while (left < right && nums[left] == nums[left + 1])
                        left++;
                    while (left < right && nums[right] == nums[right - 1])
                        right--;
                    left++;
                    right--;
                } else if ((x + nums[left] + nums[right]) < 0) {
                    left++;
                } else {
                    right--;
                }
            }
            while (i < nums.length - 2 && nums[i] == nums[i + 1])
                i++;
        }
        return res;
    }

    public static void main(String[] args) {
        int[] nums = {-1, 0, 1, 2, -1, -4};
        threeSum(nums).stream().forEach(list -> System.out.println(list.toString()));
    }
}