// 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] // ] public class 3Sum { public List> threeSum(int[] nums) { List> result = new ArrayList<>(); Arrays.sort(nums); for(int i = 0; i < nums.length - 2; i++) { if(i > 0 && nums[i] == nums[i - 1]) { continue; } int j = i + 1; int k = nums.length - 1; int target = -nums[i]; while(j < k) { if(nums[j] + nums[k] == target) { ArrayList temp = new ArrayList(); temp.add(nums[i]); temp.add(nums[j]); temp.add(nums[k]); result.add(temp); j++; k--; while(j < k && nums[j] == nums[j - 1]) { j++; } while(j < k && nums[k] == nums[k + 1]) { k--; } } else if(nums[j] + nums[k] > target) { k--; } else { j++; } } } return result; } }