# Data Structure Questions and Answers – Dynamic Array

«
»

This set of Data Structure Multiple Choice Questions & Answers (MCQs) focuses on “Dynamic Array”.

1. What is a dynamic array?
a) A variable size data structure
b) An array which is created at runtime
c) The memory to the array is allocated at runtime
d) An array which is reallocated everytime whenever new elements have to be added

Explanation: It is a varying-size list data structure that allows items to be added or removed, it may use a fixed sized array at the back end.

2. What is meant by physical size in a dynamic array?
a) The size allocated to elements
b) The size extended to add new elements
c) The size of the underlying array at the back-end
d) The size visible to users

Explanation: Physical size, also called array capacity is the size of the underlying array, which is the maximum size without relocation of data.

3. The number of items used by the dynamic array contents is its __________
a) Physical size
b) Capacity
c) Logical size
d) Random size

Explanation: The number of items used by the dynamic array contents is called logical size. Physical size is the size of the underlying array, which is the maximum size without reallocation of data.

4. How will you implement dynamic arrays in Java?
a) Set
b) Map
c) HashMap
d) List

Explanation: ArrayList is used to implement dynamic arrays in Java.

5. Which of the following is the correct syntax to declare an ArrayList in Java?
a) ArrayList al = new ArrayList();
b) ArrayList al = new ArrayList[];
c) ArrayList al() = new ArrayList();
d) ArrayList al[] = new ArrayList[];

Explanation: This is a non-generic way of creating an ArrayList.

6. Array is divided into two parts in ____________
a) Hashed Array Tree
b) Geometric Array
c) Bounded-size dynamic array
d) Sparse Array

Explanation: The first part stores the items of the dynamic array and the second part is reserved for new allocations.

7. Which of the following is a disadvantage of dynamic arrays?
a) Locality of reference
b) Data cache utilization
c) Random access
d) Memory leak

Explanation: Dynamic arrays share the advantage of arrays, added to it is the dynamic addition of elements to the array. Memory can be leaked if it is not handled properly during allocation and deallocation. It is a disadvantage.

8. What is the time complexity for inserting/deleting at the beginning of the array?
a) O(1)
b) O(n)
c) O(logn)
d) O(nlogn)

Explanation: All the other elements will have to be moved, hence O(n).

9. Dynamic arrays overcome the limit of static arrays.
a) True
b) False

Explanation: Static arrays have fixed capacity. The capacity must be specified during memory allocation. Dynamic arrays don’t require to specify their capacity during memory allocation. Dynamic arrays have fixed physical size at backend and its capacity increases if required. Thus, Dynamic arrays overcome the limit of static arrays.

10. The size of the dynamic array is deallocated if the array size is less than _________% of the backend physical size.
a) 30
b) 40
c) 10
d) 20

Explanation: The size of the dynamic array is decreased/deallocated if the actual size of the array is less than 30% of the backend physical size. This is used to avoid memory wastage.

11. Both Dynamic array and Dynamically memory allocated array are same.
a) True
b) False

Explanation: Physical size of a Dynamic array is fixed with a larger value. Dynamically memory allocated arrays are arrays whose memory is allocated at run time rather than at compile time. Dynamically memory allocated arrays don’t have physical size at the backend. Thus, Dynamic arrays and Dynamically memory allocated arrays are different.

12. In which of the following cases dynamic arrays are not preferred?
a) If the size of the array is unknown
b) If the size of the array changes after few iterations
c) If the memory reallocation takes more time i.e. expensive
d) If the array holds less number of elements

Explanation: Dynamic arrays are preferred when the size of the array is unknown during memory allocation or the size changes after few iterations or the memory reallocation is expensive. If array holds less number of elements, the physical size is reduced and reduction takes more time. In that case, we can use normal arrays instead of dynamic arrays.

13. The growth factor of ArrayList in Java is _______
a) 1
b) 1.5
c) 2
d) 0

Explanation: The growth factor of dynamic arrays (Array List) in Java is 3/2.
The new array capacity is calculated as new_array_size = (old_array_size*3)/2+1.

14. In special case, the time complexity of inserting/deleting elements at the end of dynamic array is __________
a) O (n)
b) O (n1/2)
c) O (log n)
d) O (1)

Explanation: In general, the time complexity of inserting or deleting elements at the end of dynamic array is O (1). Elements are added at reserved space of dynamic array. If this reserved space is exceeded, then the physical size of the dynamic array is reallocated and every element is copied from original array. This will take O(n) time to add new element at the end of the array.

15. Which of the following arrays are used in the implementation of list data type in python?
a) Bit array
b) Dynamic arrays
c) Sparse arrays
d) Parallel arrays 