Question

I am trying to sort an array using the insertion sort algorithm. The array is filled with WordNode elements that include a word field (inputted from a text file) and a frequency field (to measure the number of times the particular word appears in the text file). I have implemented the sort so that words are sorted by frequency (from lowest to highest), but I also want to sort alphabetically if frequencies are equal. How can I sort using two different criteria at the same time? Below is my sort code.

public static void sort(ArrayUnorderedList<WordNode> array) {
    //create stacks for insertion sort
    LinkedStack<WordNode> sorted = new LinkedStack<WordNode>();
    LinkedStack<WordNode> temp = new LinkedStack<WordNode>();

    //while the array has elements to be sorted
    while(!array.isEmpty()) {
        //remove current element from array
        WordNode currentNode = array.removeFirst();

        //while the sorted stack meets sorting criteria
        while((!sorted.isEmpty()) && (sorted.peek().getFrequency() < currentNode.getFrequency())) {
            //push elements to temp stack
            temp.push(sorted.pop());
        }

        //push current element to sorted stack
        sorted.push(currentNode);

        //while the temp stack has elements to be replaced
        while(!temp.isEmpty()) {
            //push elements to sorted stack
            sorted.push(temp.pop());
        }
    }

    //replace sorted elements in array
    while(!sorted.isEmpty()) {
        array.addToRear(sorted.pop());
    }
}

Answer 1

AppClay’s answer is absolutely correct, but if you are interested in “tidying it up”, create a helper that implements Comparator.

class WordNodeComparator implements Comparator<WordNode> {
    @Override
    public int compare(WordNode lhs, WordNode rhs) {
        int result = lhs.getFrequency() - rhs.getFrequency();
        if (result == 0) {
            return lhs.getWord().compareTo(rhs.getWord());
        }
        else {
            return result;
        }
    }
}

Then you simply create an instance of it, and use it in your loop:

while((!sorted.isEmpty()) && (nodeComparator.compare(sorted.peek(), currentNode) < 0)

Not only does this make the code easier to read and test, it’s now trivial to swap out different Comparator implementations as needed.