2309-greatest-english-letter-in-upper-and-lower-case.java

//Contest 298 brute-force feel free to share any improvements
class Solution {

    public String greatestLetter(String s) {
        HashSet<Integer> set = new HashSet<>();
        int ans = -1;
        for (int i = 0; i < s.length(); i++) {
            if (
                set.contains((s.charAt(i) - 32)) ||
                set.contains((s.charAt(i) + 32))
            ) ans = Math.max(ans, (int) Character.toUpperCase(s.charAt(i)));
            set.add(0 + s.charAt(i));
        }
        return ans == -1 ? "" : (char) ans + "";
    }
}