Java 代码

import java.util.Scanner;

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

        String s = cin.nextLine();

        String r = cin.next();

        String s2 = "";
        for (int i = 0; i < s.length(); i ++)
        {
            if (s.charAt(i) == r.charAt(0)) 
                s2 += "#";
            else
                s2 += s.charAt(i);
        }
        System.out.println (s2);
    }
}