백준(BOJ) 1157

#include <iostream>
#include <algorithm>
using namespace std;
int arr[100];
int main(void){
   char c;
   while((c = getchar()) != EOF && c != '\n'){
       if(c >= 'a') c -= 'a' - 'A';
       arr[c]++;
   }
   int result = 0;
   int res;
   bool unique = true;
   for(int i = 'A'; i <= 'Z' ; i++){
        if(result < arr[i]){
            result = arr[i];
            res = i;
            unique = true;
        }
        else if(result == arr[i]){
            unique = false;
        }
   }
   if(unique) printf("%c", res);
   else printf("?");
}