2025-08-18 17:04:04 +0000 UTC

class Solution:
    def greatestLetter(self, s: str) -> str:
        freqs = [(False, False)] * 26
        for char in reversed(s):
            if char.islower():
                idx = ord(char) - 97
                is_lower = True
            else:
                idx = ord(char) - 65
                is_lower = False
            enc_lower, enc_upper = freqs[idx]
            new_val = (enc_lower or is_lower, enc_upper or not is_lower)
            if new_val != (enc_lower, enc_upper):
                freqs[idx] = new_val
        for i in reversed(range(len(freqs))):
            if all(freqs[i]):
                return chr(i + 65)
        return ""