Change prime factor implementation to recursive

Author: mapu77

src/main/java/edu/thoughtworks/training/PrimeFactor.java

@@ -4,17 +4,27 @@
 import java.util.Collection;
 
 public class PrimeFactor {
- public Collection<Integer> generate(int input) {
- Collection<Integer> primeFactors = new ArrayList<Integer>();
- for (int i = 2; i <= Math.sqrt(input); ++i) {
- if (input % i == 0) {
- primeFactors.add(i);
- input /= i;
- }
 
- }
- if (input != 1) primeFactors.add(input);
+ private static final int FIRST_PRIME = 2;
 
+ public Collection<Integer> generate(int number) {
+ Collection<Integer> primeFactors = new ArrayList<>();
+ generate(number, FIRST_PRIME,primeFactors);
  return primeFactors;
  }
+
+ private void generate(final int number, final int possiblePrimeFactor, final Collection<Integer> primeFactors) {
+ if (number != 1) {
+ if (isDivisibleBy(number, possiblePrimeFactor)) {
+ primeFactors.add(possiblePrimeFactor);
+ generate(number/possiblePrimeFactor, possiblePrimeFactor, primeFactors);
+ } else {
+ generate(number, possiblePrimeFactor+1, primeFactors);
+ }
+ }
+ }
+
+ private boolean isDivisibleBy(final int number, final int possiblePrimeFactor) {
+ return number % possiblePrimeFactor == 0;
+ }
 }