/r/dailyprogrammer Challenge #114 Easy Solution

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.ListIterator;
import java.util.Set;


public class WordLadderEasy {
    public static String wordUrl = "words.txt";
    public static ArrayList<String> words = new ArrayList<String>();

    public final static int hamming(String a, String b) {
        if(a.length() != b.length())
            return -1;
        int r = 0;
        for(int i = 0; i < a.length(); i++)
            if(a.charAt(i) != b.charAt(i))
                r++;
        return r;
    }

    public final static void loadWords() {
        try {
            BufferedReader r = new BufferedReader(new FileReader(new File(new File(System.getProperty("user.dir")), wordUrl)));
            words.clear();
            while(r.ready())
                words.add(r.readLine());
            r.close();
        } catch (Exception e) {
        }
    }

    public final static ArrayList<String> ladder(String base) {
        if(words.size() == 0)
            loadWords();
        ListIterator<String> i = words.listIterator();
        ArrayList<String> r = new ArrayList<String>();
        while(i.hasNext()) {
            String s = i.next();
            int x = hamming(base, s);
            if(x == 1)
                r.add(s);
        }
        return r;
    }

    public final static ArrayList<String> freqLadder(int freq) {
        if(words.size() == 0)
            loadWords();
        ArrayList<String> r = new ArrayList<String>();
        ListIterator<String> i = words.listIterator();
        while(i.hasNext()) {
            String s = i.next();
            if(ladder(s).size() == freq)
                r.add(s);
        }
        return r;
    }

    public final static String findLargest() {
        String current = "";
        int currentMax = -1;
        ListIterator<String> i = words.listIterator();
        while(i.hasNext()) {
            String s = i.next();
            int x = ladder(s).size();
            if(x > currentMax) {
                currentMax = x;
                current = s;
            }
        }
        return current;
    }

    public final static int findLongest(String base, int steps) {
        Set<String> words = new HashSet<String>();
        Set<String> seen = new HashSet<String>();
        words.add(base);
        for(int i = 0; i < steps; i++) {
            Set<String> newWords = new HashSet<String>();
            for(String word : words) {
                Set<String> extended = extend(word, seen);
                seen.addAll(extended);
                newWords.addAll(extended);
            }
            words.addAll(newWords);
        }
        return words.size();
    }

    public final static Set<String> extend(String word, Set<String> seen) {
        ArrayList<String> w = ladder(word);
        for(String s : seen)
            w.remove(s);
        Set<String> s = new HashSet<String>();
        s.addAll(w);
        return s;
    }

    public static void main(String[] args) {
        loadWords();
        System.out.println(ladder("puma"));
        System.out.println(freqLadder(33));
        String max = findLargest();
        System.out.println(max + " : " + ladder(max).size());
        System.out.println("Max from \"best\" is " + findLongest("best", 3));
    }
}