Java: how to count non-repeated (occurring only once) Strings in ArrayList?

I am trying to find the number of Strings that only appear exactly once in an ArrayList.

How many I achieve this (preferably with the best possible time complexity)?

Below is my method:

  public static int countNonRepeats(WordStream words) {

    ArrayList<String> list = new ArrayList<String>();
    for (String i : words) {
      list.add(i);
    }

    Collections.sort(list);

    for (int i = 1; i < list.size(); i++) {
      if (list.get(i).equals(list.get(i - 1))) {
        list.remove(list.get(i));
        list.remove(list.get(i - 1));
      }
    }

    System.out.println(list);

    return list.size();
  }

Why doesn't it remove the String at list.get(i) and list.get(i-1)?

Here's one simple suggestion:

1. First, sort your array by alphanumerical order
2. Iterate through with a loop, if( !list.get(i).equals(list.get(i+1)) ) → unique
3. If you find duplicates, increment i until you reach a different string

This will have the complexity of the sorting algorithm, since step 2+3 should be O(n)