import java.util.Scanner; import java.util.List; import java.util.ArrayList; public class ThreeSum { private ArrayList threeSums = new ArrayList(); /** * Constructor * @param all An ArrayList containing all the elements */ public ThreeSum(List all) { if (all.size() < 3) { System.out.println("Elements are too few!"); return; } get3Sum(new ArrayList(), all); if (threeSums.size() < 1) { System.out.println("No triplets were found!"); return; } System.out.println("The 3 sums are: "); for (ArrayList threeSum : threeSums) System.out.println(threeSum); } public static void main(String[] args) { List list = new ArrayList(); //Enter the numbers in a space separated string E.g -3 2 -1 -2 0 4 3 Scanner sc = new Scanner(System.in); String[] elements = sc .nextLine().split("\\s+"); try { for (String element : elements) list .add(Integer.parseInt(element)); System.out.println("The numbers are: " + list); ThreeSum s = new ThreeSum(list); } catch (NumberFormatException e) { System.out.println("Invalid input"); } } /** * Method to get all triplets in an ArrayList * Uses recursion * @param current The current group of numbers * @param remaining The remaining numbers in the list */ public void get3Sum(List current, List remaining) { int size = current.size(); int limit = remaining.size(); switch (size) { case 0: for (int i = 0;i < limit - 1;i++) { for (int j = i + 1;j < limit;j++) { List temp = new ArrayList(); temp .add(remaining.get(i)); temp .add(remaining.get(j)); List temp2 = new ArrayList(); for (int k = j + 1;k < limit;k++) { temp2 .add(remaining .get(k)); } get3Sum(temp, temp2); } } break; case 2: int sum = 0; for (int x : current) sum += x; for (int i = 0;i < limit;i++) { int a = remaining.get(i); if (sum + a == 0) { List temp = new ArrayList(); temp.addAll(current); temp.add(a); threeSums .add((ArrayList)temp); } } break; } } }

3 Sum Challenge(Ace)