Фреквентен стринг - [хеширање]

Фреквентен стринг Problem 3 (0 / 0)

Даден е стринг. Треба да се најде најчестиот под-стринг кој е дел од него и да се испечати. Доколку два под-стринга се исто фреквентни, тогаш се печати подолгиот. Доколку и овој услов го исполнуваат тогаш се печати лексикографски помалиот.

Пример: За стрингот "abc" под-стрингови се "a", "b", "c", "ab", "bc", "abc". Сите имаат иста честота па затоа се печати најдолгиот "abc".

Име на класата (Java): MostFrequentSubstring.

package com.example;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;

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

    // Each MapEntry object is a pair consisting of a key (a Comparable
    // object) and a value (an arbitrary object).
    K key;
    E value;

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

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

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

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

    // An object of class OBHT is an open-bucket hash table, containing entries
    // of class MapEntry.
    private MapEntry<K,E>[] buckets;

    // buckets[b] is null if bucket b has never been occupied.
    // buckets[b] is former if bucket b is formerly-occupied
    // by an entry that has since been deleted (and not yet replaced).

    static final int NONE = -1; // ... distinct from any bucket index.

    private static final MapEntry former = new MapEntry(null, null);
    // This guarantees that, for any genuine entry e,
    // e.key.equals(former.key) returns false.

    private int occupancy = 0;
    // ... number of occupied or formerly-occupied buckets in this OBHT.

    @SuppressWarnings("unchecked")
    public OBHT (int m) {
        // Construct an empty OBHT with m buckets.
        buckets = (MapEntry<K,E>[]) new MapEntry[m];
    }


    private int hash (K key) {
        // Translate key to an index of the array buckets.
        return Math.abs(key.hashCode()) % buckets.length;
    }


    public int search (K targetKey) {
        // Find which if any bucket of this OBHT is occupied by an entry whose key
        // is equal to targetKey. Return the index of that bucket.
        int b = hash(targetKey); int n_search=0;
        for (;;) {
            MapEntry<K,E> oldEntry = buckets[b];
            if (oldEntry == null)
                return NONE;
            else if (targetKey.equals(oldEntry.key))
                return b;
            else
            {
                b = (b + 1) % buckets.length;
                n_search++;
                if(n_search==buckets.length)
                    return NONE;

            }
        }
    }


    public void insert (K key, E val) {
        // Insert the entry <key, val> into this OBHT.
        MapEntry<K,E> newEntry = new MapEntry<K,E>(key, val);
        int b = hash(key); int n_search=0;
        for (;;) {
            MapEntry<K,E> oldEntry = buckets[b];
            if (oldEntry == null) {
                if (++occupancy == buckets.length) {
                    System.out.println("Hash tabelata e polna!!!");
                }
                buckets[b] = newEntry;
                return;
            }
            else if (oldEntry == former
                    || key.equals(oldEntry.key)) {
                buckets[b] = newEntry;
                return;
            }
            else
            {
                b = (b + 1) % buckets.length;
                n_search++;
                if(n_search==buckets.length)
                    return;

            }
        }
    }


    @SuppressWarnings("unchecked")
    public void delete (K key) {
        // Delete the entry (if any) whose key is equal to key from this OBHT.
        int b = hash(key); int n_search=0;
        for (;;) {
            MapEntry<K,E> oldEntry = buckets[b];

            if (oldEntry == null)
                return;
            else if (key.equals(oldEntry.key)) {
                buckets[b] = former;//(MapEntry<K,E>)former;
                return;
            }
            else{
                b = (b + 1) % buckets.length;
                n_search++;
                if(n_search==buckets.length)
                    return;

            }
        }
    }


    public String toString () {
        String temp = "";
        for (int i = 0; i < buckets.length; i++) {
            temp += i + ":";
            if (buckets[i] == null)
                temp += "\n";
            else if (buckets[i] == former)
                temp += "former\n";
            else
                temp += buckets[i] + "\n";
        }
        return temp;
    }


    public OBHT<K,E> clone () {
        OBHT<K,E> copy = new OBHT<K,E>(buckets.length);
        for (int i = 0; i < buckets.length; i++) {
            MapEntry<K,E> e = buckets[i];
            if (e != null && e != former)
                copy.buckets[i] = new MapEntry<K,E>(e.key, e.value);
            else
                copy.buckets[i] = e;
        }
        return copy;
    }
}


public class Main {
    public static String MaxFreq(String str) {
        int n = str.length();

        // go delime stringot i go stavame vo mapa.
        // <String,Integer-frekventnosta>
        Map<String,Integer> hm = new HashMap<>();
        for (int i=0; i<n; i++) {
            String s = "";
            for (int j=i; j<n; j++) {
                s += str.charAt(j);
                if (hm.containsKey(s)) {
                    hm.put(s,hm.get(s) + 1);
                } else {
                    hm.put(s,1);
                }
            }
        }

        int max = 0;
        String s = "";
        for (Map.Entry<String,Integer> i : hm.entrySet()) {
            if (i.getValue() > max) {
                max = i.getValue();
                s = i.getKey();
            } else if (i.getValue() == max) {
                String ss = i.getKey();
                if (ss.length() > s.length()) {
                    s = ss;
                }
                if (ss.length() == s.length()) {
                    if (ss.compareTo(s) > 0) {
                        s = ss;
                    }
                }
            }
        }
        return s;
    }
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String str = br.readLine();
        System.out.println(MaxFreq(str));
    }
}



Simple input-1:
bab

Simple output:
b


Simple input-2:
abab

Simple output:
ab


Simple input-3:
abcd

Simple output:
abcd