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++; else hi--; } } } return re; } }