15. 3Sum

Given an array S of n integers, are there elements a, b, c in S 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.

For example, given array S = [-1, 0, 1, 2, -1, -4],A solution set is:[  [-1, 0, 1],  [-1, -1, 2]]

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public class Solution {    public List<List<Integer>> threeSum(int[] nums) {        Arrays.sort(nums);        List<List<Integer>> re = new ArrayList<>();for (int i = 0; i < nums.length - 2; ++i) {if (i == 0 || nums[i] != nums[i - 1]) {int sum = 0 - nums[i];int lo = i + 1;int hi = nums.length - 1;while (lo < hi) {if (nums[lo] + nums[hi] == sum) {List<Integer> temp = new ArrayList<>();temp.add(nums[i]);temp.add(nums[lo]);temp.add(nums[hi]);re.add(temp);while (lo < hi && nums[lo] == nums[lo + 1])lo++;while (lo < hi && nums[hi] == nums[hi - 1])hi--;lo++;hi--;} else if (nums[lo] + nums[hi] < sum)lo++;elsehi--;}}}return re;    }}