class FirstUniqueCharFinder {
  final static int ASCII_OFFSET = 97;
  final static int ALPHABET_LEN = 26;
 
  static char find(String word) {
    int[] alphabet = new int[ALPHABET_LEN];
    char[] charArray = word.toLowerCase().toCharArray();
 
    for (int codePoint: charArray) {
      int index = codePoint - ASCII_OFFSET; 
      alphabet[index]++;
    }
 
    char firstUniqueChar = 0;
 
	for (int i = 0; i < word.length(); i++) {
	  int index = charArray[i] - ASCII_OFFSET;
	  if (alphabet[index] == 1) {
	  	firstUniqueChar = word.charAt(i);
	  	break;
	  }
	}
 
    return firstUniqueChar;
  }
 
  public static void main(String[] args) {
    System.out.println(find("transaction"));
    System.out.println(find("reverse"));
    System.out.println(find("xyuxyuA"));
  }
}

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