백준 6단계 no.5

import java.util.Arrays;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        String str = sc.next();
        int[] alphaArr = new int[26];

        char[] arr = new char[str.length()];
        for (int i = 0; i < str.length(); i++) {
            if ((int) str.charAt(i) < 91) {
                arr[i] = (char) (str.charAt(i) + 32);
            } else {
                arr[i] = str.charAt(i);
            }
        }

        for (int i = 0; i < str.length(); i++) {
            alphaArr[(int)arr[i]-97] += 1;
        }

        int max = 0;
        int overlap = 0;
        int point = 0;
        for (int j = 0; j < alphaArr.length; j++) {
            if (alphaArr[j] > max) {
                max = alphaArr[j];
                point = j;
                overlap = 0;
            } else if (alphaArr[j] == max) {
                overlap++;
            }
        }

        if (overlap == 0) {
            System.out.print((char)(point+65));
        } else {
            System.out.print("?");
        }
    }
}