GATE CS 2021 Set 1 — Question 19
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Algorithms → Sorting → Bubble, Insertion, Selection Sort
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Question
Consider the following array.
Which algorithm out of the following options uses the least number of comparisons (among the array elements) to sort the above array in ascending order?
| 23 | 32 | 45 | 69 | 72 | 73 | 89 | 97 |
|---|
Correct answer
(C) Insertion sort
Solution
The given array is already sorted in ascending order. Let .
(A) Selection sort: Always performs comparisons regardless of the initial order.
(B) Mergesort: Always performs comparisons. For , it is approximately comparisons.
(C) Insertion sort: For an already sorted array, it only performs comparisons (one for each element from the second onwards to check against its predecessor).
(D) Quicksort (last element as pivot): For a sorted array, this is the worst-case scenario, resulting in comparisons.
Insertion sort uses the least number of comparisons.
(A) Selection sort: Always performs comparisons regardless of the initial order.
(B) Mergesort: Always performs comparisons. For , it is approximately comparisons.
(C) Insertion sort: For an already sorted array, it only performs comparisons (one for each element from the second onwards to check against its predecessor).
(D) Quicksort (last element as pivot): For a sorted array, this is the worst-case scenario, resulting in comparisons.
Insertion sort uses the least number of comparisons.
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