import java.util.Arrays;
 
class FirstUniqueCharFinder {
  static char find(final String word) {
    char[] charArray = word.toLowerCase().toCharArray();
 
    int[] ascii = new int[26];
    Arrays.fill(ascii, 0);
 
    for (char c : charArray) {
      int n = ((int) c) - 97;
      ascii[n]++;
    }
 
    for (char c: charArray) {
      int n = ((int) c) - 97;
      if (ascii[n] == 1) {
        return c;
      }
    }
 
    return ' ';
  }
 
  public static void main(String[] args) {
    System.out.println(find("transaction"));
    System.out.println(find("reverse"));
  }
}

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