Removing a substring from a string, repeatedly

Question

Problem: Remove the substring t from a string s, repeatedly and print the number of steps involved to do the same.

Explanation/Working:

For Example: t = ab, s = aabb. In the first step, we check if t is contained within s. Here, t is contained in the middle i.e. a(ab)b. So, we will remove it and the resultant will be ab and increment the count value by 1. We again check if t is contained within s. Now, t is equal to s i.e. (ab). So, we remove that from s and increment the count. So, since t is no more contained in s, we stop and print the count value, which is 2 in this case.

So, here's what I have tried:

1. Code 1:

   static int maxMoves(String s, String t) {
       int count = 0,i;
   
       while(true)
       {
           if(s.contains(t))
           {
               i = s.indexOf(t);
               s = s.substring(0,i) + s.substring(i + t.length());
           }
           else break;
   
           ++count;
       }
   
       return count;
   }
   

   I am just able to pass 9/14 test cases on Hackerrank, due to some reason (I am getting "Wrong Answer" for rest of the cases). After a while, I found out that there is something called replace() method in Java. So, I tried using that by replacing the if condition and came up with a second version of code.

2. Code 2:

   static int maxMoves(String s, String t) {
       int count = 0,i;
   
       while(true)
       {
           if(s.contains(t))
               s.replace(t,""); //Marked Statement
           else break;
   
           ++count;
       }
   
       return count;
   }
   

   But for some reason (I don't know why), the "Marked Statement" in the above code gets executed infinitely (this I noticed when I replaced the "Marked Statement" with System.out.println(s.replace(t,""));). I don't the reason for the same.

Since, I am passing only 9/14 test cases, there must be some logical error that is leading to a "Wrong Answer". How do I overcome that if I use Code 1? And if I use Code 2, how do I avoid infinite execution of the "Marked Statement"? Or is there anyone who would like to suggest me a Code 3?

Thank you in advance :)

Answer 1

Try saving the new (returned) string instead of ignoring it.

s = s.replace(t,"");

replace returns a new string; you seemed to think that it alters the given string in-place.