RepeatingEvenStrings.java

import java.util.*;
import java.io.*;
import java.math.*;

public class RepeatingEvenString {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String inputString = in.nextLine();
        String result = removeEvenRepeatedCharacters(inputString);
        System.out.println(result);
    }

    public static String removeEvenRepeatedCharacters(String string) {

        // if string length is less than 2, nothing needs to be done
        if (string.length() < 2) {
            return string;
        }

        // flag to denote if a change has been made
        boolean changed;

        do {
            int charIndex = 0;
            char currentChar = string.charAt(charIndex);
            changed = false;
            
            String temp = "";
            for (int i=1; i<string.length(); i++) {
                if (string.charAt(i) != currentChar) {
                    if ((i - charIndex) % 2 != 0) {
                        for(int j=charIndex; j<i; j++) {
                            temp += string.charAt(j);
                        }
                    }
                    else {
                        changed = true;
                    }
                    charIndex = i;
                    currentChar = string.charAt(charIndex);
                }
                // corner case involving the last character in the string
                else if (string.charAt(i) == currentChar && i == string.length()-1 && (charIndex - i - 1)%2 != 0) {
                    for (int j=charIndex; j<=i; j++) {
                        temp += string.charAt(j);
                    }
                }
            }
            
            // temp contains the resulting string after even repeating characters are removed in this iteration
            string = temp;
            if (string.length() < 2) break;
        }while(changed);  // if the string is changed, there is possibility of even repeating characters forming again

        return string;
    }
}