nonrepeating

 public static char findRepeating(String s){

        HashMap<Character, Integer> charCount= new HashMap<>();
        int count=0;
        for (int i=0; i<s.length(); i++){
            if (charCount.containsKey(s.charAt(i))){
                count=charCount.get(s.charAt(i));
                charCount.put(s.charAt(i), ++count);
            }
            else{
                charCount.put(s.charAt(i), 1);
            }

        }
        for (Character ch:charCount.keySet()){
            if (charCount.get(ch)==0){
                return ch;
            }
        }
        return '\0';
    }