题解 | #找出字符串中第一个只出现一次的字符#

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);
        int num = 0;
        String str = in.nextLine();
        StringBuilder str1 = new StringBuilder();
        StringBuilder str2 = new StringBuilder();
        str1.append(str.charAt(0));
        for (int i = 1; i < str.length(); i++) {
            if (str2.toString().contains(String.valueOf(str.charAt(i)))) {
                continue;
            } else if (str1.toString().contains(String.valueOf(str.charAt(i)))) {
                str2.append(str.charAt(i));
            } else
                str1.append(str.charAt(i));
        }
        for (int i = 0; i < str.length(); i++) {
            if (!str2.toString().contains(String.valueOf(str.charAt(i)))) {
                System.out.println(str.charAt(i));
                num++;
                break;
            }
        }
        if (num == 0) {
            System.out.println(-1);
        }
    }
}