编辑代码

public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str1 = sc.nextLine();
        //String str1 = "abca";
		int[] count = new int[26]; //用来存储小写字母a-z出现的次数。

		for(int i=0; i<str1.length(); i++){		
			char tmp = str1.charAt(i); //依次取出每个字母
			int index = tmp - 97; //利用ascii码表，最小结果是0.
			count[index] = count[index] + 1;
		}
		
		//循环打印每个字母出现次数
        StringBuilder str2=new StringBuilder("");
		for(int j=0; j<count.length; j++){
			if(count[j] >= 2)
                str2.append((char)(j+97));
		//System.out.println("字母"+(char)(j+97)+"出现次数："+count[j]);
	    }
        System.out.println(str2);
    }
}