删除字符串中出现次数最少的字符

import java.util.*;
 
public class Main{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        while(in.hasNext()){
            String s = in.nextLine();
            int[] a = new int[26];
            for(int i=0;i<s.length();i++){
                a[s.charAt(i)-97]++;
            }
            int min = 21;
            //找出出现最小的次数
            for(int i=0;i<26;i++){
                if(a[i]<min && a[i]>0){
                    min = a[i];
                }
            }
            StringBuilder toBeDeleted = new StringBuilder();
            for(int i=0;i<26;i++){
                if(a[i]==min){
                    char c = (char)(‘a‘+i);
                    toBeDeleted.append(c);
                }
            }
            String str = toBeDeleted.toString();
            StringBuilder res = new StringBuilder();
            for(int i=0;i<s.length();i++){
                if(!str.contains(s.charAt(i)+"")){
                    res.append(s.charAt(i));
                }
            }
            System.out.println(res);
        }
    }
     
}