# Tessellate S.T.E.M.S - Computer Science - School - Set 1 - Subjective Problem

You are given a string comprised of symbols a and b. You have to perform certain operations on it.

In each operation, you must select an occurrence of the substring ab in the string and replace it with bba. You must keep doing such operations until there is no occurrence of the string ab.

The task for this problem is to: Give an algorithm, whose input is such a string, and which computes the minimum number of operations until the string is free of occurrences of ab.

This problem is a part of Tessellate S.T.E.M.S.

1 year, 5 months ago

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What should be the time complexity of the solution?

- 1 year, 5 months ago

Try coming up with the best solution that you can :)

Staff - 1 year, 5 months ago

How do we need to answer above question? Write theory explaining the stuff or the pseudocode?

- 1 year, 5 months ago

You are expected to describe the algorithm, possibly in the form of a pseudo-code, and describe why it is correct. Also, analyze the performance of the algorithm.

Staff - 1 year, 5 months ago

So will you allot non-binary scores on subjective task according to the answer's quality? Proving the algorithm(sometimes greedy) is sometimes hard.

- 1 year, 5 months ago

So will you allot non-binary scores on subjective task according to the answer's quality?

Yes. I will check with the organizers and clarify this point.

Proving the algorithm(sometimes greedy) is sometimes hard.

I agree. However, if an algorithm designer does not prove his algorithm, how does one know that what he has proposed really does what we want it to? That said, a next best thing to a proof would be some kind of heuristic justification of why you'd think that the algorithm is correct.

Staff - 1 year, 5 months ago

"Hard problems make people think, and once in a while, it's not a horrible thing to think" - Vikraman Balaji

We stand by Balaji's words and believe that it is only through hard problems that one can assess understanding. Please give your best to the response. There will be points for the approach and the solution, and not just the answer.

Thank you On behalf of S.T.E.M.S Aalok

- 1 year, 5 months ago

can the algorithm be a computer code of c++ format like with for loops and while loops and array along with basic string functions

- 1 year, 5 months ago

– You are expected to describe the algorithm, possibly in the form of a pseudo-code, and describe why it is correct. Also, analyze the performance of the algorithm.

- 1 year, 5 months ago

1: str= stored string 2: str1="" 3: i=0 4: f=0 5: while (i< length of str) 6: c= character of str at i th position 7: if (c='a') f=f+1 8: elseif (c='b' and f>0) str1=str1+"bb" 9: elseif (c not equal to 'b' and f>0) str1=str1+'a', f=0 10: if (c not = 'a' or c not = 'b') str1=str1+c 11: i=i+1 12: end of while loop 13: return str1

- 1 year, 5 months ago

Algorithim !!!!

- 1 year, 5 months ago

- 1 year, 5 months ago

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1: str= stored string 2: str1="" 3: i=0 4: f=0 5: while (i< length of str) 6: c= character of str at i th position 7: if (c='a') f=f+1 8: elseif (c='b' and f>0) str1=str1+"bb" 9: elseif (c not equal to 'b' and f>0) str1=str1+'a', f=0 10: if (c not = 'a' or c not = 'b') str1=str1+c 11: i=i+1 12: end of while loop 13: return str1 

- 1 year, 5 months ago

- 1 year, 5 months ago

The logic is that check the number of b's after a and then replace 2x number of b's before a removing those b's

- 1 year, 5 months ago