백준 1157번: 단어 공부 (C++)

https://www.acmicpc.net/problem/1157

#pragma warning(disable :4996)
#include<iostream>
#include<string>
using namespace std;
 
int alp[26];
int main(void) {
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    string str;
    cin >> str;
    
    for (int i = 0; i < str.length(); i++) {
        if (str[i] >= 'a' && str[i] <= 'z')
            alp[str[i] - 'a']++;
        else
            alp[str[i] - 'A']++;
    }
    
    int Max = 0, idx =0;
    for (int i = 0; i < 26; i++) {
        if (Max < alp[i]) {
            idx = i;
            Max = alp[i];
        }
    }
    
    for (int i = 0; i < 26; i++) {
        if (alp[i] == Max && i != idx) {
            cout << "?";
            return 0;
        }
    }
 
    char ans = idx + 'A';
    cout << ans;
    return 0;
}