题解 | #找出字符串中第一个只出现一次的字符#

import java.util.*;
//HashSet保证字符不重复遍历，提高搜索速度
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s =in.nextLine();
        HashSet<Character> hashSet = new HashSet<>();
        String res = "";
            for(int i=0; i<s.length(); i++){
                if(hashSet.add(s.charAt(i))){
                    int temp = s.length() - s.replaceAll(s.charAt(i)+"","").length();
                    if(temp == 1){
                        System.out.print(s.charAt(i));
                        return;
                    }
                }
            }System.out.print(-1);
    }
}