String Comparison Using Nested Loops

Question

I'm following this online Java course, after every session there is few assignments, and I can't seem to solve this one.

I know that's not the point of an exercise, but I tried everything and I can't see any other way.

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Write a program that returns number of occurrences of a string in another string. For example:

Input:
First String: the

Second String: the students are working hard in the faculty of Engineering because **the**y love it

Output:
3

Note: You should use nested loops. Don’t use some methods like indexOf or substring

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This is my code so far, I know it's not complete, and I'm pretty sure most of this decisions statements aren't needed.

Edit: This is a C# code, I was testing on both Java and C#

        String Text1 = Console.ReadLine();
        String Text2 = Console.ReadLine();
        int counter = 0;

        for (int y = 0; y < Text1.Length; y++)
        {

            for (int x = 0; x < Text2.Length; x++)
            {

                if (Text1[y] == Text2[x])
                {

                    if (y + 1 < Text1.Length && x + 1 < Text2.Length)
                    {
                        if (Text1[y + 1] == Text2[x + 1])
                        {

                        }
                    }


                }

            }

        }

Answer 1

Since you are working on an exercise, I wouldn't fix your code, but help you fix it yourself.

First, some basics: in Java you use charAt(i) to access an individual character. For example,

char ch = Text1.charAt(3);

gets you the forth character from the beginning of the string (indexes are zero-based).

Now for the algorithm: you want to iterate through all positions of the second string with enough characters after it to make a match with the first string possible. This means that the index goes from zero, inclusive, to the position Text2.length()-Text1.length(), exclusive. This is the starting position of the potential match - let's call it p.

Given a position p, you want to iterate through all characters of Text1 starting at zero, and compare them to Text2 characters starting with the character at position p. Let's say the index in Text1 is called i, and it goes from zero, inclusive, to Text1.length(), exclusive. Then you want to compare Text1.getChar(i) for equality with Text1.charAt(i+p).

You need to finish the comparison with all characters of Text1 before you declare a match. You need to know the result in the outer loop, so you want to use a bool flag. Set the flag to true before the inner loop. If you see a mismatch, set the flag to false, and break out of the loop.

If the flag is true after the inner loop, increment the counter.

Answer 2

public static int count(String text1, String text2)
{
    int res = 0;
    for (int i=0;i<text2.length()-text1.length();i++)
    {
       if (text1.charAt(0) == text2.charAt(i))
       {
          boolean found = true;
          for (int j=0;j<text1.length() && found;j++)
              if (text1.charAt(j) != text2.charAt(i+j))
                  found = false;
          if (found)
              res++;
       }
    }
    return res;
}

Answer 3

@Mody- As this is an assignment, I suggest you to follow "public int indexOf(String str)" method in String.class and replicate something similar with little modification to solve your problem.