How do I solve the todo's for this code

package algs52; // section 5.2
import java.util.HashSet;
import stdlib.*;

// Create a spell checker that find all "misspelled" words (e.g. non-existing words).
// Compare performance of the TST and Trie on various dictionary sizes.

// Download and install the following files into your algs4/data directory:
// - https://introcs.cs.princeton.edu/java/data/commonwords.txt 74K words
// - https://introcs.cs.princeton.edu/java/data/wordlist.txt 224K words
// - https://introcs.cs.princeton.edu/java/data/words.utf-8.txt 645K words
//
// Expected output should be similar in performance:
//
// TrieST | TST
// Words Time | Words Time %
// 23699 0.40 | 23699 0.18 43%
// 25913 0.53 | 25913 0.34 63%
// 18075 1.15 | 18075 0.86 74%


public class hw4
{
public static HashSet<string> TrieFilter(String dictionary_file, String text_file)
{
// TODO: Create a Trie from the dictionary, and find all non-existing words in the input text file.

HashSet<string> filteredWords = new HashSet<>();
return filteredWords;
}

public static HashSet<string> TSTFilter(String dictionary_file, String text_file)
{
// TODO: Create a TST from the dictionary, and find all non-existing words in the input text file.

HashSet<string> filteredWords = new HashSet<>();
return filteredWords;
}

private static void runTest(String dictionary, String textfile)
{
Stopwatch stopwatch = new Stopwatch();
HashSet<string> f1 = TrieFilter(dictionary, textfile);
double t1 = stopwatch.elapsedTime();

stopwatch = new Stopwatch();
HashSet<string> f2 = TSTFilter(dictionary, textfile);
double t2 = stopwatch.elapsedTime();

StdOut.printf("%10d %6.2f | %10d %6.2f %4d%%\n", f1.size(), t1, f2.size(), t2, (int)(100*(t2/t1)));
}

public static void main(String[] args)
{
String commonwords = "data/commonwords.txt";
String wordlist = "data/wordlist.txt";
String words = "data/words.utf-8.txt";
String textfile = "data/mobydick.txt";

StdOut.printf("%20s %16s\n", "TrieST | ", "TST");
StdOut.printf("%20s %20s\n", "Words Time | ", "Words Time %");

runTest(commonwords, textfile);
runTest(wordlist, textfile);
runTest(words, textfile);
}
}

What I have tried:

<pre>if(filteredWords.contains(text_file)){
			
			filteredWords.add(text_file);

		}
		return filteredWords;

		}