数组哈希表
import java.util.*;
class Main
{
public static void main(String[] args)
{
Scanner sc=new Scanner(System.in);
int[] mp=new int[26];
String s=sc.next();
int maxx=-1;
for(char x:s.toCharArray())
{
mp[x-'A']++;
maxx=Math.max(maxx,mp[x-'A']);
}
for(int i=0;i<26;i++)
if(mp[i]==maxx) System.out.print((char)('A'+i));
}
}
TreeMap
import java.util.*;
class Main
{
public static void main(String[] args)
{
Scanner sc=new Scanner(System.in);
TreeMap<Character,Integer> mp=new TreeMap<>();
String s=sc.next();
int maxx=-1;
for(char x:s.toCharArray())
{
mp.put(x,mp.getOrDefault(x,0)+1);
maxx=Math.max(maxx,mp.get(x));
}
for(Map.Entry<Character,Integer> x:mp.entrySet())
if(x.getValue()==maxx) System.out.print(x.getKey());
}
}