public class Solution {
  public String deDup(String input) {
    // Write your solution here.
    if (input == null || input.length() <= 1) {
      return input;
    }
    char[] array = input.toCharArray();
    int slow = 0;
    for (int fast = 1; fast < array.length; fast++) {
      if (slow == -1 || array[slow] != array[fast]) {
        array[++slow] = array[fast];
      } else {
        while (fast + 1 < array.length && array[fast] == array[fast + 1]) {
          fast++;
        }
        slow--;
      }
    }
    return new String(array, 0 , slow + 1);
  }
}