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.stream.*;

// 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);
        // 注意 hasNext 和 hasNextLine 的区别
        String line = in.nextLine();
        List<Character> list = new ArrayList<>();
        for(Character c : line.toCharArray()){
            list.add(c);
        }
        Map<Character ,Long> map = list.stream().collect(Collectors.groupingBy(a -> a ,Collectors.counting()));
        Set<Character> set = map.entrySet().stream().filter(entry -> entry.getValue() > 1).map(Map.Entry::getKey).collect(Collectors.toSet());
        list.removeAll(set);
        if(list.size() == 0){
            System.out.println(-1);
        }else{
            System.out.println(list.get(0));
        }
    }
}