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    List Processing and In-Place Mutation PYQs for GATE DA

    Solve 2+ List Processing and In-Place Mutation previous year questions for GATE DA with answers and detailed solutions. Free sample questions below.

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    Question 1
    2026 PYQ
    Level 3: Exam Standard
    Consider the given Python program.

    def fun(L, i=0):
        if i >= len(L)-1:
            return 0
        if L[i] > L[i+1]:
            L[i+1], L[i] = L[i], L[i+1]
            return 1+fun(L, i+1)
        else:
            return fun(L, i+1)

    data = [5, 3, 4, 1, 2]
    count = 0
    for _ in range(len(data)):
        count += fun(data)
    print(count)

    The output of the program is __________ . (Answer in integer)
    Question 2
    2024 PYQ
    Level 3: Exam Standard
    Consider the following Python function:
    def fun(D, s1, s2):
    if s1 < s2:
    D[s1], D[s2] = D[s2], D[s1]
    fun(D, s1+1, s2-1)
    What does this Python function fun() do? Select the ONE appropriate option
    below.
    Free preview ends here

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    List Processing and In-Place Mutation PYQs for GATE DA

    Solve 2+ List Processing and In-Place Mutation previous year questions for GATE DA with answers and detailed solutions. Free sample questions below.

    Chapter Roadmap: List Processing and In-Place Mutation

    Chapter Roadmap

    Chapter journey

    1. Recursive List Processing and In-Place Mutation
      Current topic. High-importance tracing.
      • Single-index recursive scans
      • Adjacent-swap counting
      • Two-pointer reversal
    2. Chapter mastery
      • Track exact list state after every swap
      • Decide if call is scan or reversal
      • Predict final return value and list
    Weight hint: Core tracing topic. Small code pieces can carry good marks through careful step-by-step execution.

    Topic Hero: Recursion Meets Mutable Lists

    Topic Hero: Recursion Meets Mutable Lists

    A Python list is mutable. If a recursive function changes the list, the changed list is visible to all deeper recursive calls.

    Two core shapes appear repeatedly:

    Shape Indices used Typical operation
    Single-index scan i Compare and possibly swap L[i] and L[i+1]
    Two-pointer reversal s1, s2 Swap D[s1] and D[s2], then move inward
    Key idea: The list is shared, but the index variables are local to each recursive call.

    List Processing and In-Place Mutation: Solved Questions with Step-by-Step Explanations (2 Problems)

    Question 1 · Programming, Data Structures and Algorithms · 2026 NAT
    Consider the given Python program.

    def fun(L, i=0):
        if i >= len(L)-1:
            return 0
        if L[i] > L[i+1]:
            L[i+1], L[i] = L[i], L[i+1]
            return 1+fun(L, i+1)
        else:
            return fun(L, i+1)

    data = [5, 3, 4, 1, 2]
    count = 0
    for _ in range(len(data)):
        count += fun(data)
    print(count)

    The output of the program is __________ . (Answer in integer)
    Correct Answer:

    8.00

    Step-by-Step Solution

    Insight: The inner function fun performs one left-to-right pass of adjacent swaps, returning the number of swaps. The outer loop calls it n times, which is exactly the Bubble Sort algorithm. The total number of swaps in Bubble Sort equals the number of inversions in the initial array.

    Exam route: Count the inversions in [5, 3, 4, 1, 2]. 5 is greater than 3, 4, 1, 2 (4 inversions). 3 is greater than 1, 2 (2 inversions). 4 is greater than 1, 2 (2 inversions). Total = 4 + 2 + 2 = 8.

    Learning route:

    Pass 1: [5, 3, 4, 1, 2] -> 5 bubbles to the end. Swaps: (5,3), (5,4), (5,1), (5,2). Count = 4. Array: [3, 4, 1, 2, 5].

    Pass 2: [3, 4, 1, 2, 5] -> 4 bubbles to index 3. Swaps: (4,1), (4,2). Count = 2. Array: [3, 1, 2, 4, 5].

    Pass 3: [3, 1, 2, 4, 5] -> 3 bubbles to index 2. Swaps: (3,1), (3,2). Count = 2. Array: [1, 2, 3, 4, 5].

    Pass 4 & 5: Already sorted, 0 swaps.

    Total count = 4 + 2 + 2 + 0 + 0 = 8.

    Question 2 · Programming, Data Structures and Algorithms · 2024 MCQ
    Consider the following Python function:
    def fun(D, s1, s2):
    if s1 < s2:
    D[s1], D[s2] = D[s2], D[s1]
    fun(D, s1+1, s2-1)
    What does this Python function fun() do? Select the ONE appropriate option
    below.
    1. A.

      It finds the smallest element in D from index s1 to s2, both inclusive.

    2. B.

      It performs a merge sort in-place on this list D between indices s1 and s2, both inclusive.

    3. C.

      It reverses the list D between indices s1 and s2, both inclusive.

    4. D.

      It swaps the elements in D at indices s1 and s2, and leaves the remaining elements unchanged.

    Correct Answer:

    C

    Step-by-Step Solution

    Insight: The function swaps the elements at s1 and s2, then recursively calls itself with s1+1 and s2-1. This is the standard two-pointer recursive reversal pattern.

    Exam route: Recognize the two pointers moving inwards (s1+1, s2-1) and swapping elements. This reverses the subarray from s1 to s2.

    Learning route:

    Base case: s1 < s2 is false (i.e., s1 >= s2), it stops.

    Recursive step: swaps D[s1] and D[s2], then moves pointers inward.

    This exactly reverses the segment D[s1...s2] in place.

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