Merkkijono

import java.util.*;
/*
 * Datatähti 2018
 * Tuomas Karjalainen, Nurmeksen lukio
 */
public class Merkkijono {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    String line = input.nextLine();
    int[] arr = new int[line.length()];
    for (int i=0; i<line.length(); i++) {
      arr[i] = (int) line.charAt(i);
    }

    boolean changed = false;
    do {
      int previousValue = arr[0];
      int previousPos = 0;
      changed = false;

      for (int i=1; i<arr.length; i++) {
        if (arr[i] == 0) continue;
        if (arr[i] == previousValue) {
          previousValue = arr[i];
          arr[previousPos] = 0;
          arr[i] = 0;
          changed = true;
        } else if(changed) {
          break;
        } else {
          previousValue = arr[i];
        }
        previousPos = i;
      }
    } while (changed);

    // Return the array
    for (int i=0; i < arr.length; i++) {
      if (arr[i] != 0)
        System.out.print((char) arr[i]);
    }
    System.out.print('\n');
  }
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED