题解 | #找出字符串中第一个只出现一次的字符#

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();

        LinkedHashMap<Character, Integer> hm = new LinkedHashMap<>();
        for (char c : str.toCharArray()) {
            hm.put(c, hm.getOrDefault(c, 0) + 1);
        }

        Character t = ' ';
        for (Character m : hm.keySet()) {
            if (hm.get(m) == 1) {
                t = m;
                break;
            }
        }
        if (t != ' ') System.out.println(t);
        else System.out.println(-1);
    }
}