First uniqie character in a string

First unique character in a string Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

//Input : loveleetcode

private int firstUniqueCharacterArrayApproach(String str) {
        //loveleetcode, but the problem is unordered map
        int arr [] = new int[26];
        for (int i =0; i < str.length(); i++) {
            int ch = str.charAt(i) - 'a';
            arr[ch]++;  //maintain character frequency
        }
        for (int i =0; i < str.length(); i++) {
            if(arr[str.charAt(i) - 'a'] == 1) {
                return i;
            }
        }
        return -1;
    }

    private int firstUniqueCharacterMapApproach(String str) {
        //loveleetcode, but the problem is unordered map, for this we need a iterate over a array again 
        Map<Character, Integer> frequencyMap = new HashMap<>();
        for (int i =0; i < str.length(); i++) {
            frequencyMap.put(str.charAt(i), frequencyMap.getOrDefault(str.charAt(i), 0)+1);
        }
        for (int i =0; i < str.length(); i++) {
            if(frequencyMap.get(str.charAt(i)) == 1) {
                return i;
            }
        }
        return -1;
    }