Sorting Algorithms
Übersicht
Hand a shuffled pack of cards to two people and tell them both to put it in order. One of them goes through the pack again and again, swapping any neighbouring pair that is the wrong way round, until a whole pass produces no swaps at all. The other splits the pack in half, gives half to a friend, and when the two sorted halves come back merges them by repeatedly taking whichever of the two top cards is lower. Both finish with a sorted pack. On fifty-two cards they finish at about the same time. On fifty-two thousand they do not.
Those are the bubble sort and the merge sort, and this specification asks for something different from each. For the bubble sort you must know one specific version, with two nested loops, and be able to follow and write pseudocode for it. For the merge sort you must be able to explain it in prose and demonstrate it on a given set of data, and you will not be asked to write pseudocode for it. Then you must compare and contrast the two. Knowing which of those three demands applies to which algorithm saves you from revising the wrong thing.
Ziele
- Understand and explain how the merge sort algorithm works.
- Understand and explain how the bubble sort algorithm works.
- Compare and contrast merge sort and bubble sort algorithms.
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- In the version of the bubble sort required by this specification, what controls the outer loop? A. A count of the number of items B. A count of the number of swaps made C. Whether any swaps were made during the previous pass D. Whether the first element is smaller than the last Answer: C
- An array of 6 items is already in ascending order. How many passes does the bubble sort make? A. 1 B. 5 C. 6 D. 15 Answer: A
- Which statement about the merge sort is correct? A. It compares each element with the one next to it B. It splits the list in half repeatedly and then merges the sorted pieces C. It only works on data that is already partly sorted D. It sorts in place without needing any extra memory Answer: B
- Two sorted lists, 2, 5, 9 and 3, 4, are merged. Which value is taken third? A. 2 B. 3 C. 4 D. 5 Answer: C
- Which of these is an advantage of the bubble sort over the merge sort? A. It is much faster on very large lists B. Its performance does not depend on the starting order C. It detects an already sorted list in a single pass D. It can sort lists that do not fit in memory Answer: C
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