CSC300: Linked structures: Cautious, backward recursion [8/17] Previous pageContentsNext page

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  public int numFives () {
    if (first == null) return 0;
    return numFivesH (first);
  }
  private static int numFivesH (Node x) {
    int result = (x.next == null) ? 0 : numFivesH (x.next);
    if (x.item == 5) result = result + 1;
    return result;
  }
call@3 ([5,11,5,5])
  call@4 ([11,5,5])
    call@5  ([5,5])
      call@6  ([5])
      retn@6  ([5]) : 1
    retn@5  ([5,5]) : 2
  retn@4 ([11,5,5]) : 2
retn@3 ([5,11,5,5]) : 3

A more verbose version:

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  public int numFives () {
    if (first == null) return 0;
    return numFivesH (first);
  }
  private static int numFivesH (Node x) {
    int result = 0;
    if (x.next != null) {
      result = numFivesH (x.next);
    }
    if (x.item == 5) result = result + 1;
    return result;
  }

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