[АПС] Фреквентен стринг

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Comparator;

class MapEntry<K extends Comparable<K>,E> implements Comparable<K> {

    K key;
    E value;

    public MapEntry (K key, E val) {
        this.key = key;
        this.value = val;
    }

    public int compareTo (K that) {
        @SuppressWarnings("unchecked")
        MapEntry<K,E> other = (MapEntry<K,E>) that;
        return this.key.compareTo(other.key);
    }

    public String toString () {
        return "(" + key + "," + value + ")";
    }
}

class SLLNode<E> {
    protected E element;
    protected SLLNode<E> succ;

    public SLLNode(E elem, SLLNode<E> succ) {
        this.element = elem;
        this.succ = succ;
    }

    @Override
    public String toString() {
        return element.toString();
    }
}

class CBHT<K extends Comparable<K>, E> {

    private SLLNode<MapEntry<K,E>>[] buckets;

    @SuppressWarnings("unchecked")
    public CBHT(int m) {
        buckets = (SLLNode<MapEntry<K,E>>[]) new SLLNode[m];
    }

    private int hash(K key) {
        return Math.abs(key.hashCode()) % buckets.length;
    }

    public SLLNode<MapEntry<K,E>> search(K targetKey) {
        int b = hash(targetKey);
        for (SLLNode<MapEntry<K,E>> curr = buckets[b]; curr != null; curr = curr.succ) {
            if (targetKey.equals(((MapEntry<K, E>) curr.element).key))
                return curr;
        }
        return null;
    }

    public void insert(K key, E val) {      // Insert the entry <key, val> into this CBHT.
        MapEntry<K, E> newEntry = new MapEntry<K, E>(key, val);
        int b = hash(key);
        for (SLLNode<MapEntry<K,E>> curr = buckets[b]; curr != null; curr = curr.succ) {
            if (key.equals(((MapEntry<K, E>) curr.element).key)) {
                curr.element = newEntry;
                return;
            }
        }
        buckets[b] = new SLLNode<MapEntry<K,E>>(newEntry, buckets[b]);
    }

    public void delete(K key) {
        int b = hash(key);
        for (SLLNode<MapEntry<K,E>> pred = null, curr = buckets[b]; curr != null; pred = curr, curr = curr.succ) {
            if (key.equals(((MapEntry<K,E>) curr.element).key)) {
                if (pred == null)
                    buckets[b] = curr.succ;
                else
                    pred.succ = curr.succ;
                return;
            }
        }
    }

    public String toString() {
        String temp = "";
        for (int i = 0; i < buckets.length; i++) {
            temp += i + ":";
            for (SLLNode<MapEntry<K,E>> curr = buckets[i]; curr != null; curr = curr.succ) {
                temp += curr.element.toString() + " ";
            }
            temp += "\n";
        }
        return temp;
    }

}

class MostFrequentSubstring {

    public static boolean isPrime(int m){
        for(int i = 2; i < Math.sqrt(m); i++)
            if(m % i == 0)
                return false;

        return true;
    }

    public static int findM(int n){
        int m = (int)(n / 0.6);
        while (!isPrime(m))
            m++;
        return m;
    }

    public static void main (String[] args) throws IOException {
        CBHT<String,Integer> tabela = new CBHT<String,Integer>(300);
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String word = br.readLine().trim();

        /*
        *
        * Vashiot kod tuka....
        *
        */
        int n = word.length()*(word.length()-1)/2;
        CBHT<String, Integer> sub = new CBHT<>(findM(n));
        String substring;
        String mostFrequent = "zaba";
        int max = 0;

        for(int i = 1; i <= word.length(); i++){
            for(int j = 0; j < i; j++){

                substring = word.substring(j, i);
                SLLNode<MapEntry<String, Integer>> daliPostoi = sub.search(substring);
                if(daliPostoi == null)
                    sub.insert(substring, 1);
                else {
                    sub.insert(substring, daliPostoi.element.value+1);
                }
                int l = sub.search(substring).element.value;
                if(l > max){
                    mostFrequent = substring;
                    max = l;
                }
                else if(l == max){
                    if(substring.length() > mostFrequent.length())
                        mostFrequent = substring;
                    else if(substring.length() == mostFrequent.length()){
                        int k = substring.compareTo(mostFrequent);
                        if(k < 0)
                            mostFrequent = substring;
                    }
                }

            }
        }
        System.out.println(mostFrequent);

    }
}