How to Remove Duplicates from a String in Java Using Hashing?

Working with strings is a typical activity in Java programming, and sometimes we need to remove duplicate characters from a string. Using hashing is one effective way to do this. By assigning a unique hash code to each element, hashing enables us to keep track of unique items. This article will examine the use of hashing in Java to eliminate duplicates from a string.

Approach

Preserving a set of unique characters is the primary motivation for using hashing to eliminate duplicates from a string. The hash code for each character in the string may be found by iterating over it and storing unique characters in a hash set. We effectively filter out duplicates by doing this.

Example to Remove Duplicates from a String in Java Using Hashing

Let’s look at a simple example in which we want to use hashing to eliminate duplicates from the term “programming”.

Java

// Java Program to Remove Duplicates
// From a String in Java Using Hashing
import java.util.HashSet;

// Driver Class
public class RemoveDuplicatesExample {
    public static String removeDuplicates(String input) {
        HashSet<Character> uniqueChars = new HashSet<>();
        StringBuilder result = new StringBuilder();

        for (char ch : input.toCharArray()) {
            if (uniqueChars.add(ch)) {
                // Character is unique,
                  // add it to the result
                result.append(ch);
            }
        }

        return result.toString();
    }

    public static void main(String[] args) {
        String inputString = "programming";
        String result = removeDuplicates(inputString);

        System.out.println("Original String: " + inputString);
        System.out.println("String after removing duplicates: " + result);
    }
}

Output

Original String: programming
String after removing duplicates: progamin

Explanation of the above Program:

• The removeDuplicates function stores unique characters observed in a HashSet (uniqueChars) after receiving a string as input.
• It uses add() to run over each character in the input text and determine whether or not it already exists in the HashSet.
• The character is added to the StringBuilder result if it is unique.
• Converting the StringBuilder to a string yields the desired outcome.