Скачать или смотреть Properly Count the Number of Insertion Sort Comparisons in Java

Learn how to accurately count comparisons in `insertion sort` with proper techniques and avoid common pitfalls in your Java implementation.
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This video is based on the question https://stackoverflow.com/q/64184425/ asked by the user 'Alexa Jenasoba' ( https://stackoverflow.com/u/12033719/ ) and on the answer https://stackoverflow.com/a/64184783/ provided by the user 'YourHelper' ( https://stackoverflow.com/u/14105130/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Insertion Sort Comparisons

Insertion sort is a widely used sorting algorithm that builds the final sorted array one item at a time. However, when implementing this algorithm in Java, counting the comparisons accurately can become a challenge. In this guide, we will explore how to count the number of insertion sort comparisons correctly and identify any misconceptions you might have.

The Problem

You may find yourself in a situation where your counted comparisons during insertion sort do not match the expected results. For instance, consider the following input arrays:

Input { 9, 5, 6, 7, 2, 8 } where the expected number of comparisons is 11, but you get 13.

Input { "how", "about", "dey", "da", "bears" } expecting 7, however, you observe 8.

This discrepancy raises the question: Are your expectations incorrect, or is there an issue in the counting mechanism within your Java implementation?

The Solution

The primary source of misunderstanding often lies in how you are counting the comparisons. Let’s break down the issue and clarify the counting method.

The Key Logic in Counting Comparisons

In the insertion sort implementation provided, you are using the following snippet to count comparisons:

[[See Video to Reveal this Text or Code Snippet]]

Important Observations

Double Counting:

The comparison is evaluated in the while loop condition (comp.compare(input[j - 1], input[j]) > 0). If the loop condition fails, it still increments the comparisons counter in the last line of the loop where it checks again for the comparison outside the loop. This can lead to incorrect counts especially when elements are already in order or when no swaps are needed.

Fixing the Count:

Remove the comparisons+ + outside the loop. This will ensure that you're only counting comparisons where a swap is necessary.

Here’s a corrected version of the code:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Accurately counting comparisons in insertion sort not only aids in understanding the algorithm's efficiency but also helps you improve your coding accuracy in Java. By ensuring that comparisons are counted correctly—only when necessary—you can avoid discrepancies like those observed in the example inputs.

Now that you know how to appropriately count comparisons, it’s time to apply these techniques in your Java projects and validate your sorting algorithms more effectively!