Selection Sort MCQs: Solved Questions with Explanations for GATE and Govt Exams

Selection sort appears often in objective papers because its comparison count, swap count, greedy nature and in-place behaviour all make clean MCQs. Selection sort is relevant to GATE CS aspirants, government CS and IT paper takers, including DSSSB, BPSC, UP Police computer operator and ISRO candidates, as well as placement-test candidates. A fixed set of invariants connects comparisons, swaps, complexity, dry runs and C-code recognition, so one clear mental model answers all 11.

1. Sixty-second refresher: how selection sort actually works

After pass k, the first k positions contain the k smallest elements in final sorted order. In pass i, where i runs from 0 to n-2, the algorithm scans positions i through n-1, finds the minimum and swaps it into position i.

There is at most one swap per pass, so there are at most n-1 swaps. The comparison count is fixed:

(n-1) + (n-2) + ... + 1 = n(n-1)/2

For n = 5, this is 5 x 4 / 2 = 10 comparisons, whatever the input order. The fixed comparison count, limited swaps and placement of the smallest elements explain the answers.

2. Concept MCQs: what selection sort is

Q1. Repeatedly finding the minimum

This question is from TPSC 2025.

Which of the following sorting algorithms is based on the concept of repeatedly finding the minimum element ?

• Quick Sort

• Selection Sort

• Bubble Sort

• Merge Sort

Selection sort literally selects the minimum in every pass. Bubble sort compares adjacent pairs, quick sort partitions around a pivot, and merge sort divides and merges.

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Q2. Match the description

This question is from BELPRO 2025.

Which of the following best describes the working of Selection Sort?

• Divide and conquer strategy.

• Compare adjacent elements and swap if needed.

• Merge smaller subarrays recursively.

• Select the smallest element and place it at the beginning.

The second option describes bubble sort, while the first and third point towards merge sort. The final option is the exact selection sort operation.

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Q3. Design technique

This question is from ISRO 2007 and BEL 2007.

The design technique used by the Selection Sort algorithm is an example of:

• Greedy method

• Divide-and-conquer

• Dynamic Programming

• Backtracking

Each pass makes the locally best choice by taking the current minimum, then never revisits that fixed position. This commit-and-never-undo pattern is greedy.

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3. Advantage MCQs: why anyone still uses it

Q4. The distinguishing advantage

This question is from BPSC 2024.

Which of the following is the biggest advantage of selection sort?

• it has low time complexity

• it has low space complexity

• it requires at most n-1 swaps under any condition

• More than one of the above

• None of the above

Its time complexity is O(n^2), so the first option is false. O(1) extra space is useful but is shared by other simple sorts. The distinguishing advantage is at most n-1 writes, valuable when writes to storage such as flash memory or EEPROM are expensive. Therefore, “More than one” is a trap.

Q5. Read the offered options

This question is from Goldman Sachs 2023.

What is the advantage of selection sort over other sorting techniques?

• It requires no additional storage space

• It is scalable

• It works best for inputs which are already sorted

• It is faster than any other sorting technique

In this option set, in-place O(1) extra storage is the only true advantage. Selection sort is not adaptive, so an already sorted input still takes n(n-1)/2 comparisons. Compare Q4 and Q5 carefully: the correct advantage depends on the choices offered.

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4. Complexity MCQs: the GATE favourites

Q6. Overall complexity

This question is from DSSSB 2021.

What is the complexity of selection sort algorithms?

• O(n)

• O(n log2 n)

• O(n^2)

• O(2n)

Comparisons dominate. Their sum is (n-1) + (n-2) + ... + 1 = n(n-1)/2, which is Theta(n^2). Sortedness changes nothing, so this holds in the best, average and worst cases.

Q7. Tightest upper bound on swaps

This question is associated with GATE 2013. It is also associated with BARC 2013.

Which one of the following is the tightest upper bound that represents the number of swaps required to sort n numbers using selection sort?

• O(log n)

• O(n)

• O(n log n)

• O(n^2)

There is at most one swap in each of n-1 passes, so the tightest offered upper bound is O(n). The larger bounds are upper bounds too, but they are not tight.

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Q8. Worst-case swaps

This question is from GATE 2009.

What is the number of swaps required to sort n elements using selection sort, in the worst case? (A) Theta(n) (B) Theta(n log n) (C) Theta(n^2) (D) Theta(n^2 log n)

Correct: A, Theta(n).

Pair this with Q7. Worst-case swaps are Theta(n), but comparisons are Theta(n^2). Memorise the exact pair: comparisons n(n-1)/2, swaps at most n-1.

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5. Dry-run MCQs: trace it on paper

Q9. Count the swaps

This question is from UP Police 2023.

How many swaps are needed to sort the array {3, 1, 5, 2, 4} using Selection Sort ?

• 2

• 3

• 4

• 5

Trace every pass:

1. Swap 3 and 1: [1, 3, 5, 2, 4]

2. Swap 3 and 2: [1, 2, 5, 3, 4]

3. Swap 5 and 3: [1, 2, 3, 5, 4]

4. Swap 5 and 4: [1, 2, 3, 4, 5]

All four passes need a swap. Since n = 5 and n-1 = 4, this input reaches the maximum. The trace exactly matches the diagram above.

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Q10. Stop after the third pass

This question is from DSSSB 2021.

Sort the following list using the selection sort algorithm. H, V, A, T, L, N, K. What is the output of the algorithm after the 3rd pass?

• A, V, H, T, L, N, K

• A, H, K, T, L, N, V

• A, V, T, H, L, N, K

• A, T, H, K, L, N, V

Pass 1 chooses A and swaps it with H: A, V, H, T, L, N, K. Pass 2 chooses H and swaps it with V: A, H, V, T, L, N, K. Pass 3 chooses K and swaps it with V: A, H, K, T, L, N, V.

Use the checkpoint trick. After pass 3, the first three entries must be the three smallest letters, A, H and K, in order. That eliminates three options immediately.

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6. Code-reading MCQ: recognise it in C

Q11. What does the complete loop do?

This question is associated with placement papers from 2024 and 2025. The same code is also associated with CoCubes.

What purpose does the following code serve

int main() {
    int array[] = {5, 3, 1, 9, 8, 2, 4, 7};
    int size = sizeof(array)/sizeof(array[0]);
    int i, j, min_idx, temp;
    for (i = 0; i < size-1; i++) {
        min_idx = i;
        for (j = i+1; j < size; j++) {
            if (array[j] < array[min_idx])
                min_idx = j;
        }
        temp = array[min_idx];
        array[min_idx] = array[i];
        array[i] = temp;
    }
}

• Finds some specific element in the array

• Sort the elements of array

• Find the smallest element in the array

• None of the above

Look for the fingerprint: an outer loop to size-1, a min_idx updated during the inner scan, and one swap after that scan. One outer iteration finds a minimum, but repeating it for every position sorts the array. That is why “Find the smallest element” is the trap.

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7. The five facts that answer almost every selection sort MCQ

For stability, consider [4a, 4b, 2]. The first pass swaps 4a with 2, producing [2, 4b, 4a]. The equal 4s have changed relative order, so standard array selection sort is not stable.

For a wider view, compare it with other methods in Sorting Algorithms: Complexity and Comparison. GATE aspirants should also keep the response formats straight with MCQ, MSQ or NAT? GATE Question Types Explained.

8. The short version and where to practise next

Selection sort accepts extra comparisons in return for very few writes. Know n(n-1)/2 comparisons and at most n-1 swaps cold, and most objective questions take under a minute.

About 15 Selection Sort questions are available for practice, including 11 with explanations. Descriptive questions also ask for every pass or pseudocode, so practise writing the trace rather than only choosing an option.

For structured DSA practice with PYQs inside the course player, continue with DSA using Java: Placement Preparation Course or DSA Using Python. To browse the wider subject shelf, use Coding & DSA Courses for Placements.