[백준][Java] 1157번 단어 공부

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
 
 
public class Main {
        
    private static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    private static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
    
    public static void main(String[] args) throws IOException{
        // 어떻게 할 것인가.
        String input = br.readLine().toUpperCase();
        char[] charInput = input.toCharArray();
        int[] aToZ = new int[26];
        char result=' ';
        int max = 0;
        
        for(int i=0; i<charInput.length; i++) {
            aToZ[charInput[i]-'A']++;
        }
        
        for(int i=0; i<aToZ.length; i++) {
            if(max<aToZ[i]) {
                max=aToZ[i];
                result=(char)(i+'A');
            }
            else if(max==aToZ[i])  result='?';
        }
        
        
        
        bw.write(String.valueOf(result));
        bw.flush();
        
        
        
    }
}