Find the first un-repeated character in a string

Question

What is the quickest way to find the first character which only appears once in a string?

Answer 1

Here is one more solution with o(n) time complexity.

public void findUnique(String string) {
    ArrayList uniqueList = new ArrayList<>();
    int[] chatArr = new int[128];
    for (int i = 0; i < string.length(); i++) {
        Character ch = string.charAt(i);
        if (chatArr[ch] != -1) {
            chatArr[ch] = -1;
            uniqueList.add(ch);
        } else {
            uniqueList.remove(ch);
        }
    }
    if (uniqueList.size() == 0) {
        System.out.println("No unique character found!");
    } else {
        System.out.println("First unique character is :" + uniqueList.get(0));
    }
}