Anagrams and Palindromes examples in Java 8

In this post:

  • anagram example in Java
    • check two words are they anagrams
    • extract anagrams from list
  • palindrome example
    • palindrome - by using StringBuilder reverse method
    • palindrome - with iteration

You can check also Anagrams and Palindromes in Python

Anagrams with Java 8

Anagrams are any words or sentences whose scrambled letters create a different word or phrase. Two strings, phrases or sentences are called anagrams if they contain same set of characters but in different order.

Several examples:

ASTRONOMER -> MOON STARER
ELEVEN PLUS TWO -> TWELVE PLUS ONE
DORMITORY -> DIRTY ROOM

Check two words if they are anagrams

Code example in Java checking if two words are anagrams:

public static void main(String[] args) {
    System.out.println(isAnagram("face", "cafe"));
    System.out.println(isAnagram("face", "caffe"));
}

public static Boolean isAnagram(String word1, String word2){
    List<String> listWord1 = new ArrayList<>(Arrays.asList(word1.split("")));
    List<String> listWord2 = new ArrayList<>(Arrays.asList(word2.split("")));
    
    Collections.sort(listWord1);
    Collections.sort(listWord2);
    
    word1 = String.join("", listWord1);
    word2 = String.join("", listWord2);
    
    //return listWord1.equals(listWord2);
    return word1.equals(word2);
    //return word1 == word2 ; // not working because == tests for reference equality
}

What is doing this code.

  • first we convert the words to lists of characters
  • then lists are being sort in alphabetical order
  • finally we convert the list back to string
  • compare the result with method equals and return the result

result:

true
false

Extract anagrams from list:

Let say that you have a given list of words and you want to extract all groups of anagrams. Then you can use this code example in java:

public static void main(String[] args) {
    List<String> wordList = Arrays.asList("face", "caffe", "cafe", "milk", "limk", "abc");
    
    extractAnagrams(wordList);
}

public static void extractAnagrams(List<String> wordList){
    Map<String,List<String>> map = new HashMap<>();
    wordList.forEach(word -> map.put(anagramize(word), listWords(word, map) ));
    for (Map.Entry<String, List<String>> entry : map.entrySet()) {
        System.out.println("key : " + entry.getKey() + " word : " + entry.getValue());
    }
    System.out.println("Anagrams from list: " + wordList);
    for (Map.Entry<String, List<String>> entry : map.entrySet()) {
        if(entry.getValue().size() > 1) {
            System.out.println(entry.getValue());
        }
    }
}
public static String anagramize(String word){
    List<String> listWord = new ArrayList<>(Arrays.asList(word.split("")));
    Collections.sort(listWord);
    return String.join("", listWord);
}
public static List<String> listWords(String word, Map<String,List<String>>  map){
    List<String> arrayList = map.getOrDefault(anagramize(word), new ArrayList<>(Arrays.asList()));
    arrayList.add(word);
    return arrayList;
}

the result of this code is:

key : iklm word : [milk, limk]
key : abc word : [abc]
key : aceff word : [caffe]
key : acef word : [face, cafe]
Anagrams from list: [face, caffe, cafe, milk, limk, abc]
[milk, limk]
[face, cafe]

Palindromes with Java 8

Palindrome is a word or phrase that reads the same way - backwards and forwards. Palindromes are anagrams which differs from an anagram because it requires specific order. Checking if a word is a palindrome is much easier than anagrams.

Examples:

  • RADAR
  • RACECAR
  • CIVIC
  • NOON

palindrome - by using StringBuilder reverse method

Sample java 8 code which is checking if a word is a palindrome:

public static void main(String[] args) {
    System.out.println(isPalindrome("banana"));
    System.out.println(isPalindrome("ana"));
}
public static Boolean isPalindrome(String word){
    String rev = new StringBuilder(word).reverse().toString();
    return word.equals(rev);
    //return word == rev ; // not working because == tests for reference equality
}

result:

false
true

palindrome by iteration

You can use iteration if you want to check if a word is a palindrome or not. In the next example we are going to use numbers and show how to iterate and reverse a number:

public static void main(String[] args) {
    System.out.println(numberPalindrome(1011));
    System.out.println(numberPalindrome(10101));
}

public static Boolean numberPalindrome(int number){
    int temp = number;
    int rev = 0;
    while(number>0) {
        int dig = number % 10;
        rev = rev * 10 + dig;
        number = number/10;
    }
    return temp == rev;
}

result:

false
true

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