java:所谓滑、动、窗、口，有什么用？多此一举的感觉

import java.util.Scanner;

public class Main {

         public static void main(String[] args) {

                Scanner in = new Scanner(System.in);

                String s1 = in.next();

                String s2 = in.next();

                int windowSize= in.nextInt();

                int s1l=s1.length();

                int s2l=s2.length();

                s1=s1+'a';                ？？？？？？？？？

                s2=s2+'b';                ？？？？？？？？？

                int i,j,k;

                int big,max=0;

                int flag1=0,flag2=0;

                for(i=0;i

                        for(j=0;j

                                big=0;

                                for(k=1;k<=windowSize;k++){                                         if((s1.substring(i,i+k)).equals(s2.substring(j,j+k)))

                                                big++;

                                        else

                                                break;

                                 }

                                if(big>max){

                                        flag1=i;

                                        flag2=j;

                                        max=big;

                                }

                        }     

                }

                big=0;                ？？？？？？？？

                while((s1.substring(flag1,flag1+big)).equals(s2.substring(flag2,flag2+big))){

                        big++;  

                }

                System.out.print(s1.substring(flag1,flag1+big-1)+"n");

        }

}