Java 代码

import java.util.Scanner;

public class Main
{
    public static void main(String[] args)
    {
        Scanner cin = new Scanner(System.in);

        String line = cin.next();

        int[] freq = new int[26];

        for (int i = 0; i < line.length(); i++)
        {
            freq [(int)line.charAt(i) - (int)'a'] += 1;
        }

        boolean found = false;
        for (int i = 0; i < line.length(); i++)
        {
            if (freq [(int)line.charAt(i) - (int)'a'] == 1)
            {
                found = true;
                System.out.println(line.charAt(i));
                break;
            }
        }

        if (! found)
            System.out.println("no");
    }
}