GATE DA 2024: Question Number 41 1 Master Paper: Question 41 Figure 1: Question Description Screenshot from the master question paper GATE Answer Key: C My Opinion: There is no correct answer for the given question as question is based on certain assumption which is not given in the question. Explanation: Here, we have given the Python function as: 1 1 def fun (D , s1 , s2 ) : 2 if s1 < s2 : 3 D [ s1 ] , D [ s2 ]= D [ s2 ] , D [ s1 ] 4 fun (D , s1 +1 , s2 -1) Listing 1: Python Function This is a recursive function. When we call the function f un ( D, s 1 , s 2) then it checks whether the index s 1 is strictly less than s 2 or not. If s 1 < s 2 then the event of tuple unpacking happens and the value of D [ s 2] assigns/copies to D [ s 1] and the value of D [ s 1] assigns/copies to D [ s 2] Basically we are swapping the values of D [ s 1] and D [ s 2] with their respective positions using the tuple unpacking. Now, we increment the index s 1 by one i.e. s 1 + 1 and decrement the in- dex s 2 by one i.e. s 2 − 1 and recursively calls f un ( ) i.e. f un ( D, s 1 + 1 , s 2 − 1) again. It happens until s 1 ≥ s 2 2 Evidences in the support of no correct option Here, there are three possible cases for calling the given Python function f un ( D, s 1 , s 2) Case 1: s 1 > s 2 : As we have seen the above Python function f un ( ) will work if s 1 < s 2 but here we are considering s 1 > s 2 and so, the statements in the ”if” condition will not be executed and it will return the D as it is. Counter-Example 1 def fun (D , s1 , s2 ) : 2 if s1 < s2 : 3 D [ s1 ] , D [ s2 ]= D [ s2 ] , D [ s1 ] 4 fun (D , s1 +1 , s2 -1) 5 6 D =[5 ,7 ,2 ,1 ,1 ,9 , -4 , -2 ,0] 7 fun (D ,8 ,2) 8 print ( D ) 9 # # Output : [5 , 7 , 2 , 1 , 1 , 9 , -4 , -2 , 0] Listing 2: Python Function fun(.) when s 1 > s 2 Output: [5 , 7 , 2 , 1 , 1 , 9 , − 4 , − 2 , 0] Here, in question, it is not given that what is ”D”, it could be any data structure to store the information like dictionary, list etc but it is mentioned in options 2 ( B ) and ( C ) that D is a list, so here we are assuming the input D as a python list as: Index Value 0 5 1 7 2 2 3 1 4 1 5 9 6 -4 7 -2 8 0 Now, when we call the Python function f un ( D, 8 , 2) where s 1 = 8 and s 2 = 2 that implies s 1 > s 2 and so, in the function f un ( ) , no statements in the ”if” condition will be executed and hence we get the same input as output. Now, we will look at the given options one by one: (A) It finds the smallest element in D from index s 1 to s 2 , both inclusive. This is not the correct option. The reason is that given function f un ( D, s 1 , s 2) is not returning anything. It is only doing the modification in D by its recursive definition. (B) It performs a merge sort in-place on this list D between indices s 1 and s 2 , both inclusive. This is not the correct option. Because it is cleared from the above counter- example that values in the list D are not sorted and we are getting the same input as output. (C) It reverses the list D between indices s 1 and s 2 , both inclusive. This is not the correct option. Because it is cleared from the above counter- example that values are not reversed in the list D and we are getting the same input as output. (D) It swaps the element in D at indices s 1 and s 2 , and leaves the remain- ing elements unchanged. This is not the correct option. Because in the input list, we have ele- ment 2 at index 2 and the element 0 at index 8. After executing the function 3 f un ( ) , we have an output list where we have element 2 at index 2 and the element 0 at index 8. Therefore, elements are swapped at indices s 1 and s 2 Hence, no option is correct for the above counter-example and so, if we assume the case that s 1 > s 2 then no option will be correct. Case 2: s 1 < s 2 : Now, in this case, the statements in the ”if” condition will be executed and so as per the above explanation about f un ( D, s 1 , s 2) , it reverses the list D be- tween indices s 1 and s 2 , both inclusive. Hence, if we assume that s 1 < s 2 then option ( C ) will be correct. Case 3: s 1 = s 2 : Now, in this case, the statements in the ”if” condition will not be executed and so option ( C ) will not be correct because we can’t get the ”elements” be- tween two indices s 1 and s 2 Hence, if we assume that s 1 = s 2 then option ( C ) will not be correct. 3 Python Code Implementation: The following Python Code is executed on the Jupyter Notebook with Python 3 kernel that indicates that no option is correct here: 4 Final Remark As we have already seen that no option will be correct if we assume the indices as s 1 > s 2 because then the statements will not not be executed in the ”if” condition for the given f un ( D, s 1 , s 2) and we get the same input as output. Hence, I am kindly requesting you, to please drop this question from the evaluation and please give MARKS TO ALL because the ques- tion is based on the assumption that s 1 < s 2 which is not mentioned in the question and if we assume s 1 > s 2 then no option will be correct. 4 Figure 2: Python Code Implementation 5 References 1. Python for Data: Data Wrangling with Pandas, NumPy, and IPython by Wes Mckinney, Publisher: O’Reilly Media, Inc. 2. Think Python, 2nd edition by Allen B. Downey, Publisher: Green Tea Press 3. Python 3 Documentation, Python Doc 5