WGU C949 — Data Structures and Algorithms I
Original Practice Questions 3 versions
1. A program must store a collection of items where the most recently
added item is always the first one removed. Which ADT matches this
requirement?
A. Queue
B. Stack
C. Set
D. Dictionary
B. Stack
A stack follows LIFO (Last-In, First-Out) ordering, where the most recently
pushed item is the first popped. Queues are FIFO, sets are unordered with no
duplicates, and dictionaries store key-value pairs .
2. Which operation removes the front item from a queue?
A. Pop
B. Push
C. Dequeue
D. Peek
C. Dequeue
Dequeue removes and returns the front element of a queue. Push and pop
are stack operations. Peek returns the front element without removing it .
3. What is the primary characteristic of a set ADT?
A. Ordered collection allowing duplicates
B. Unordered collection with no duplicates
,C. Key-value pair storage
D. Priority-based removal
B. Unordered collection with no duplicates
A set stores distinct items with no defined order. Bags allow duplicates, lists
maintain order, and dictionaries store key-value pairs .
4. Which data structure is most appropriate for a print spooler that
processes jobs in arrival order?
A. Stack
B. Queue
C. Priority queue
D. Binary search tree
B. Queue
A print spooler processes jobs in the order they were submitted, which is FIFO
behavior provided by a queue .
5. A call center routes incoming calls to the next available agent.
Which ADT models this behavior?
A. Stack
B. Queue
C. Priority queue
D. Set
B. Queue
Calls are handled in arrival order, which is FIFO. A queue ensures the earliest
call is answered first .
6. What is the time complexity of the push operation on a stack
implemented with a linked list?
A. O(1)
B. O(log n)
,C. O(n)
D. O(n²)
A. O(1)
Pushing onto a linked-list stack only requires updating the head pointer and
the new node's next reference .
7. What is the time complexity of the pop operation on a stack
implemented with an array?
A. O(1)
B. O(log n)
C. O(n)
D. O(n²)
A. O(1)
Popping from an array-based stack simply decrements the top index, a
constant-time operation .
8. In a queue implemented with a linked list, which operation is O(1)
when both head and tail references are maintained?
A. Enqueue at the rear
B. Searching for a value
C. Accessing the middle element
D. Sorting the queue
A. Enqueue at the rear
With a tail reference, enqueue appends to the tail in O(1). Searching and
middle access require O(n) traversal .
9. A binary search tree contains keys 25, 15, 35, 10, 20, 30, 40. Which
key is the inorder predecessor of 30?
A. 20
B. 25
, C. 35
D. 40
B. 25
The inorder predecessor is the next smaller key. Since 30 has no left child, the
predecessor is the lowest ancestor whose right subtree contains 30, which is
25 .
10. What is the result of inserting keys 60, 40, 80, 20, 50 into an empty
BST, then performing preorder traversal?
A. 20, 40, 50, 60, 80
B. 60, 40, 20, 50, 80
C. 20, 50, 40, 80, 60
D. 80, 60, 50, 40, 20
B. 60, 40, 20, 50, 80
Preorder visits root, left subtree, right subtree. Root 60, then left subtree (40,
20, 50), then right subtree (80) .
11. What is the result of inserting keys 60, 40, 80, 20, 50 into an empty
BST, then performing postorder traversal?
A. 20, 40, 50, 60, 80
B. 60, 40, 20, 50, 80
C. 20, 50, 40, 80, 60
D. 80, 60, 50, 40, 20
C. 20, 50, 40, 80, 60
Postorder visits left subtree, right subtree, root. Left subtree: 20, 50, 40. Right
subtree: 80. Root: 60 .
12. Which tree traversal is used to produce a sorted list from a binary
search tree?
Original Practice Questions 3 versions
1. A program must store a collection of items where the most recently
added item is always the first one removed. Which ADT matches this
requirement?
A. Queue
B. Stack
C. Set
D. Dictionary
B. Stack
A stack follows LIFO (Last-In, First-Out) ordering, where the most recently
pushed item is the first popped. Queues are FIFO, sets are unordered with no
duplicates, and dictionaries store key-value pairs .
2. Which operation removes the front item from a queue?
A. Pop
B. Push
C. Dequeue
D. Peek
C. Dequeue
Dequeue removes and returns the front element of a queue. Push and pop
are stack operations. Peek returns the front element without removing it .
3. What is the primary characteristic of a set ADT?
A. Ordered collection allowing duplicates
B. Unordered collection with no duplicates
,C. Key-value pair storage
D. Priority-based removal
B. Unordered collection with no duplicates
A set stores distinct items with no defined order. Bags allow duplicates, lists
maintain order, and dictionaries store key-value pairs .
4. Which data structure is most appropriate for a print spooler that
processes jobs in arrival order?
A. Stack
B. Queue
C. Priority queue
D. Binary search tree
B. Queue
A print spooler processes jobs in the order they were submitted, which is FIFO
behavior provided by a queue .
5. A call center routes incoming calls to the next available agent.
Which ADT models this behavior?
A. Stack
B. Queue
C. Priority queue
D. Set
B. Queue
Calls are handled in arrival order, which is FIFO. A queue ensures the earliest
call is answered first .
6. What is the time complexity of the push operation on a stack
implemented with a linked list?
A. O(1)
B. O(log n)
,C. O(n)
D. O(n²)
A. O(1)
Pushing onto a linked-list stack only requires updating the head pointer and
the new node's next reference .
7. What is the time complexity of the pop operation on a stack
implemented with an array?
A. O(1)
B. O(log n)
C. O(n)
D. O(n²)
A. O(1)
Popping from an array-based stack simply decrements the top index, a
constant-time operation .
8. In a queue implemented with a linked list, which operation is O(1)
when both head and tail references are maintained?
A. Enqueue at the rear
B. Searching for a value
C. Accessing the middle element
D. Sorting the queue
A. Enqueue at the rear
With a tail reference, enqueue appends to the tail in O(1). Searching and
middle access require O(n) traversal .
9. A binary search tree contains keys 25, 15, 35, 10, 20, 30, 40. Which
key is the inorder predecessor of 30?
A. 20
B. 25
, C. 35
D. 40
B. 25
The inorder predecessor is the next smaller key. Since 30 has no left child, the
predecessor is the lowest ancestor whose right subtree contains 30, which is
25 .
10. What is the result of inserting keys 60, 40, 80, 20, 50 into an empty
BST, then performing preorder traversal?
A. 20, 40, 50, 60, 80
B. 60, 40, 20, 50, 80
C. 20, 50, 40, 80, 60
D. 80, 60, 50, 40, 20
B. 60, 40, 20, 50, 80
Preorder visits root, left subtree, right subtree. Root 60, then left subtree (40,
20, 50), then right subtree (80) .
11. What is the result of inserting keys 60, 40, 80, 20, 50 into an empty
BST, then performing postorder traversal?
A. 20, 40, 50, 60, 80
B. 60, 40, 20, 50, 80
C. 20, 50, 40, 80, 60
D. 80, 60, 50, 40, 20
C. 20, 50, 40, 80, 60
Postorder visits left subtree, right subtree, root. Left subtree: 20, 50, 40. Right
subtree: 80. Root: 60 .
12. Which tree traversal is used to produce a sorted list from a binary
search tree?
