This set of Data Structures & Algorithms Multiple Choice Questions & Answers (MCQs) focuses on “LSD Radix Sort”.

1. Which of the following is the distribution sort?
a) Heap sort
b) Smooth sort
c) Quick sort

Explanation: In Distribution sort the inputted values are distributed to multiple intermediate structures which are then combined and placed on the output. And LSD radix sort distributes values into buckets based on the digits within values, so it is a distribution sort.

2. What is the worst case time complexity of LSD radix sort?
a) O(nlogn)
b) O(wn)
c) O(n)
d) O(n + w)

Explanation: Time complexity of LSD radix sort depends upon the word size and the number on items. It runs in O(wn) time in worst case, where n is the number of inputted elements and w is the number of digits in the largest number.

3. LSD radix sort requires _____ passes to sort N elements.
a) (w/logR)
b) N(w/logR)
c) (w/log(RN))
d) (wN/log(N))

Explanation: LSD radix sort sorts the N elements in (w/logR) passes where w is the number of digits in largest number and R(radix) is extra space required for performing the sorting operation.

4. Which of the following is false?
a) LSD radix sort is an integer sorting algorithm
b) LSD radix sort is a comparison sorting algorithm
c) LSD radix sort is a distribution sort
d) LSD radix sort uses bucket sort

Explanation: LSD radix sort uses bucket sort for grouping the keys based on the digits at that value. And as it grouped the keys based on the digits at that values, it is integer sorting algorithm.

5. Which of the following sorting algorithm is stable?
a) Heap sort
b) Selection sort

Explanation: In LSD radix sort after sorting the multiple elements with the same key will be in the same order as they were in the input array. So LSD radix sort is stable sort.

6. LSD radix sort is faster than comparison sorts.
a) True
b) False

Explanation: LSD radix sort is faster than comparison sorts when the word size is less than logn. But LSD radix sort runs slowly for elements with larger word size and smaller radix.

7. Which of the following should be used to sort a huge database on a fixed-length key field?
a) Insertion sort
b) Merge sort
d) Quick sort

Explanation: LSD radix requires only w passes to sort a fixed-length string, where w is a length of the strings. So, LSD radix sort is best suited to sort a huge database on a fixed-length key field.

8. Which of the following is a combination of LSD and MSD radix sorts?
d) Flash sort

Explanation: Forward radix sort combines the advantages of LSD and MSD radix sort. Forward radix sort inspects a complete horizontal strip at a time just like LSD radix sort.

9. Which of the following is true for the LSD radix sort?
a) works best for variable length strings
b) accesses memory randomly
c) inner loop has less instructions
d) sorts the keys in left-to-right order

Explanation: LSD radix sort sorts the keys in right-to-left order, working with Least Significant Digit first. The inner loop has a lot of instructions and LSD radix sort is used to sort fixed-length strings.

10. LSD radix sort is in-place sorting algorithm.
a) False
b) True

Explanation: LSD radix is not an in-place sorting algorithm. It needs extra memory to store the elements in bucket and its worst case space complexity is O(w + R).

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