Question

Ok so say I have a function that looks for a specific word in a custom LinkedList class:

public LinkedList find(String word) {
    if (this.word.equals(word))
        return this;
    if (next==null)
        return null;
    if (next.find(word)==next)
        return next;
    return null;
}

This code works fine, however it returns the FIRST found object that matches the criteria. What if I wanted to return the LAST object found that matches the paramater? I’m having a hard time figuring this out. Keep in mind I want to use recursion.

EDIT: What would be wrong with this code:

public LinkedList findLast(String word) {
    LinkedList temp=new LinkedList(word, null);
    if (next==null && next.word.equals(word))
        return next;
    if (next==null && !next.word.equals(word))
        temp=next.findLast(word);
    return temp;
}

Answer 1

Well, think of it this way: you need to recurse right to the end of the list, and then let the return value bubble up.

So the start of your method should either be a recursive call to look further down the list, or noting that we’re at the end of the list – which is equivalent to the “further” result being null.

Now when you’re returning, there are three options:

• You’ve already found a match later than the current point – so return that reference
• You’ve not found a match (so the return value of the recursive call was null) and:
  • The current point’s word matches – so return the current point
  • The current point doesn’t match – so return null

Hopefully that should be enough to get you to an implementation – if not, please ask more questions. I’d rather not give a full implementation when this is presumably homework.