Radix Sort Interview Questions and Answers

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Radix Sort is the sorting technique that sorts the elements by processing the digits one by one. It takes either the largest element or the smallest element of an array based on the processing of the digits. The following are the most common problems on radix sort.

Radix Sort Interview Questions and Answers

Following are the top interview questions on the radix sort:

1. What is Radix Sort?

Radix Sort is a sorting algorithm that sorts elements by processing their digits one by one. It starts the sorting by selecting the least or highest digit number in the array.

2. What's the time and space complexity of Radix Sort?

• Time complexity: O(d(n+k)), where d is the number of digits, n is the number of elements, and k is the range of values.
• Space complexity: O(n+k) due to the extra storage needed.

3. When is Radix Sort better than comparison-based sorting algorithms?

Radix sort is better when the range of numbers isn't too large and the number of digits is small.

4. What are the two types of Radix Sort?

• LSD (Least Significant Digit) -- Starts sorting from the rightmost digit.
• MSD (Most Significant Digit) -- Starts sorting from the leftmost digit.

5. Difference between LSD and MSD from Radix Sort.

• LSD sorts from the small digit element first (right to left).
• MSD sorts from the large digit elements first (left to right).

6. Can Radix Sort handle floating-point numbers?

Radix sort can handle the floating-point numbers. It is also needed for decimals and negative numbers.

7. What's the main advantage of Radix Sort?

It can run in near-linear time when the number of digits is small.

8. What data structure does Radix Sort use?

Radix Sort uses a counting sort or buckets to sort individual digits. However, these data structures are rarely used.

9. Is Radix Sort stable?

Radix sort is a stable algorithm because it maintains the original order of equal elements.

10. What types of data work best with Radix Sort?

Radix sort uses numbers as integers or floating-point and strings that can be broken into components.

11. Why isn't Radix Sort as popular as QuickSort?

It needs extra memory, isn't as cache-friendly, and doesn't work well for all data types.

12. How does Radix Sort handle negative numbers?

A common approach is to separate positive and negative numbers, sort them separately, and then merge them.

13. What does "radix" mean in Radix Sort?

It refers to the base of the numbering system. For example, it uses 10 for decimal and 2 for binary.

14. How does changing the radix affect performance?

• A larger radix means fewer sorting passes but higher memory use.
• A smaller radix means more passes but lower memory use.

15. Can Radix Sort be parallelized?

Radix sort can be parallelized efficiently because digits are processed independently.

16. How is Radix Sort different from Counting Sort?

Counting Sort works in one pass for a known range, while Radix Sort repeatedly sorts digits.

17. How do you use Radix Sort for sorting strings?

Sort characters from right to left, just like sorting numbers by digits.

18. What's the best-case time complexity of Radix Sort?

The best, worst, and average cases are all O(d(n+k)) because every digit must be processed.

19. Does Radix Sort need to know the input size before sorting?

No, but it does need to know the largest number of digits in the input.

20. How is Radix Sort different from Bucket Sort?

• Bucket Sort groups elements into buckets based on their value range.
• Radix Sort sorts based on individual digits and repeatedly uses Bucket or Counting Sort.