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 array is already sorted in ascending order, with .
- (A) Selection sort always compares every remaining pair while searching for the minimum: comparisons.
- (B) Mergesort on sorted input: each merge of two sorted halves stops when the left half is exhausted, so a merge of two runs of length costs comparisons. Total comparisons.
- (C) Insertion sort on sorted input compares each new element only with its predecessor: comparisons.
- (D) Quicksort with the last element as pivot is in its worst case on sorted input: comparisons.
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