尝试设计一个函数：hasCheated（String s1，String s2，int N）求值

Question

I got this question: A professor wants to see if two students have cheated when writing a paper. Design a function : hasCheated(String s1,String s2, int N) that evaluates to true if two strings have a common substring of length N. Additional question after implementation. Assume you don't have the possibility of using String.contains() and String.substring(). How would you implement this?

this is how I am trying to solve it:

public class exercise {


    public static void main(String[] args){
        String s1 ="";
        String s2 = "";
        int n=0;

        boolean s3;
        for(int i=0; i<=s1.length();i++){
            if(i+n <=s1.length()){
                if(s3=s1.contains(s2.substring(i, i+n)));

                System.out.printf("HasCheated\n ",s3);
                //return true;
            }
        }

        //return false;


    }


}

My Quiz is, I am doing the correct thing? Thanks in advance.

Answer 1

First change this: <=s1.length() to <s1.length() , otherwise you will get an ArrayOutOfIndex Exception.

You can use indexOf() .

Answer 2

So Basically this would be my approach:

@Pritam is right if you want to do it that way, but, assuming you don't have the possibility of using String.contains() and String.substring(). This is how i would do it.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class exercise{
public static void main(String[] args) {

    String s1="home";
    String s2="homework";
    int n=4;
    exercise p=new exercise();

    if(p.hasCheated(s1, s2, n))
    {
        System.out.println("Student Cheated ");
        return;
    }

    System.out.println("Not Cheated");



}

public boolean hasCheated(String s1,String s2, int N)
{
    boolean s3=true;
    ArrayList<String> al=new ArrayList<String>();
    ArrayList<String> bl=new ArrayList<String>();

    al.addAll(getInfo(s1,N));
    bl.addAll(getInfo(s2,N));
    al.retainAll(bl);
    if(al.size()==0)
    {
        s3=false;
    }
    return s3;

}

public List<String> getInfo(String s,int n)
{
    ArrayList<String> inf=new ArrayList<String>();
    inf.clear();
    String myStr=Arrays.toString(s.split("(?<=\\G.{4})"));

    Scanner sc=new Scanner(myStr).useDelimiter(",");
    while(sc.hasNext())
    {
        String myString=sc.next().replaceAll("\\W", "");

        inf.add(myString);
    }

    return inf;
}


}

Answer 3

1. by your logic, it would make more sens to write

    if(s3=s2.contains(s1.substring(i, i+n))); 

   since you are iterating through your first sprint, you are trying to figure out if any of the substrings of length N in s1 is contained in s2.

2. You boolean is not necessary, it does not add any value to the code.

    public hasCheated(String s1, String s2, int n){ for(int i=0; i < s1.length; i++){ if(i + n < s1.length){ if(s2.contains(si.substring(i,i+n))){ return true; } } } return false } 

Without contains or substring, you could use indexOf() as Pritam mentioned, but you would still need to replace the substring. To do so, you couls convert your string to charArray and work with indexes. It does increase the complexity.

public hasCheated(String s1, String s2, int n){
  char[] tempCharArray;
  char[] charString = s1.toCharArray();
  String comparedString = "";
  for(int i=0; i < s1.length; i++){
    if(i + n < s1.length){
      for(int j = 0; j<n ; j++){
        tempCharArray[j] = charString[i+j];
      }
      comparedString = String(tempCharArray);
      if(s2.indexOf(comparedString) > 0){
        return true;
      }
    }
  }
  return false
}

I havn't looked closely at my code, or if any better methods existed, but this would work