题解 | #找出字符串中第一个只出现一次的字符#

import java.util.*;
import java.util.Scanner;

// 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 in = new Scanner(System.in);
        String str = in.nextLine();
        HashMap<Character, Integer> hashMap = new HashMap<>();
        for (int i = 0; i < str.length(); i++) {
            hashMap.put(str.charAt(i), hashMap.getOrDefault(str.charAt(i), 0) + 1);
        }
        LinkedList<Map.Entry<Character, Integer>> entrySet = new LinkedList<>(hashMap.entrySet());
        entrySet.sort(new Comparator<Map.Entry<Character, Integer>>() {
            @Override
            public int compare(Map.Entry<Character, Integer> o1,
                               Map.Entry<Character, Integer> o2) {
                return o1.getValue().compareTo(o2.getValue());
            }
        });
        boolean ifOnce = true;
        for (int i = 0; i < str.length(); i++) {
            if (hashMap.get(str.charAt(i)) == 1) {
                System.out.println(str.charAt(i));
                ifOnce = false;
                break;
            }
        }
        if (ifOnce) System.out.println(-1);
    }
}