Data Structures & Algorithms for Competitive Exam Prep

Data Structures & Algorithms

Q. In a singly linked list, how do you insert a new node at the beginning?

A. Create a new node and point it to the head
B. Point the head to the new node
C. Insert at the end
D. None of the above

Solution

To insert a new node at the beginning, create a new node and set its next pointer to the current head.

Correct Answer: A — Create a new node and point it to the head

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Q. In a singly linked list, how do you reverse the list?

A. Swap elements
B. Use a stack
C. Iterate and change pointers
D. Use recursion

Solution

To reverse a singly linked list, you can iterate through the list and change the next pointers of each node.

Correct Answer: C — Iterate and change pointers

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Q. In a singly linked list, what is the time complexity of inserting a new node at the beginning?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

Inserting a new node at the beginning of a singly linked list is done in constant time, O(1).

Correct Answer: A — O(1)

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Q. In a singly linked list, what is the time complexity to insert an element at the beginning?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

Inserting an element at the beginning of a singly linked list is done by adjusting the head pointer, which takes constant time, O(1).

Correct Answer: A — O(1)

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Q. In a stack implemented using an array, what happens when you try to push an element onto a full stack?

A. The element is added
B. The stack overflows
C. The stack shrinks
D. The element is ignored

Solution

Pushing onto a full stack results in a stack overflow error, as there is no space to add more elements.

Correct Answer: B — The stack overflows

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Q. In a stack implemented using an array, what is the time complexity of the push operation?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

The push operation in a stack implemented with an array is O(1) as it adds an element to the top of the stack.

Correct Answer: A — O(1)

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Q. In a stack, what happens when you try to pop an element from an empty stack?

A. Returns null
B. Throws an exception
C. Returns 0
D. Does nothing

Solution

Popping from an empty stack typically throws an exception to indicate that the operation cannot be performed.

Correct Answer: B — Throws an exception

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Q. In a stack, what is the time complexity of accessing the top element?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

Accessing the top element of a stack is done in constant time, O(1), as it simply involves returning the last added element.

Correct Answer: A — O(1)

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Q. In a stack, what is the time complexity of checking if it is empty?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

Checking if a stack is empty is done in constant time, O(1), as it only requires checking the size or the top pointer.

Correct Answer: A — O(1)

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Q. In a stack, what is the time complexity of the 'top' operation?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

The 'top' operation in a stack, which retrieves the top element without removing it, has a time complexity of O(1).

Correct Answer: A — O(1)

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Q. In a stack, what is the time complexity of the pop operation when implemented using a dynamic array?

A. O(1)
B. O(n)
C. O(log n)
D. O(n^2)

Solution

The pop operation in a stack implemented using a dynamic array takes O(1) time, as it simply removes the top element.

Correct Answer: A — O(1)

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Q. In a stack, what will be the output of popping an element from an empty stack?

A. Null
B. Error
C. 0
D. Undefined

Solution

Popping an element from an empty stack typically results in an error, as there are no elements to remove.

Correct Answer: B — Error

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Q. In a stack, what will be the result of popping an element from an empty stack?

A. Return null
B. Throw an exception
C. Return 0
D. Return -1

Solution

Popping an element from an empty stack typically throws an exception, indicating that the operation cannot be performed.

Correct Answer: B — Throw an exception

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Q. In a stack, which operation is performed in constant time?

A. Push
B. Pop
C. Peek
D. All of the above

Solution

All operations (Push, Pop, and Peek) in a stack are performed in constant time, O(1).

Correct Answer: D — All of the above

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Q. In a stack, which operation is performed last?

A. Push
B. Pop
C. Peek
D. None of the above

Solution

In a stack, the last operation performed is Pop, which removes the most recently added element.

Correct Answer: B — Pop

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Q. In a stack, which operation is used to remove the top element?

A. Enqueue
B. Dequeue
C. Push
D. Pop

Solution

The operation used to remove the top element from a stack is called 'Pop'.

Correct Answer: D — Pop

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Q. In a tree structure, which traversal method is typically used for searching?

A. BFS
B. DFS
C. Both BFS and DFS
D. Neither BFS nor DFS

Solution

Both BFS and DFS can be used for searching in a tree structure, depending on the specific requirements.

Correct Answer: C — Both BFS and DFS

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Q. In a tree, which traversal method is equivalent to a level order traversal?

A. DFS
B. BFS
C. In-order
D. Pre-order

Solution

Level order traversal of a tree is equivalent to BFS, as it visits nodes level by level.

Correct Answer: B — BFS

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Q. In a weighted graph, if all edge weights are equal, which algorithm can be used to find the shortest path?

A. Dijkstra's algorithm
B. Breadth-First Search
C. Depth-First Search
D. A* algorithm

Solution

If all edge weights are equal, Dijkstra's algorithm is still applicable, but Breadth-First Search (BFS) can also be used to find the shortest path.

Correct Answer: B — Breadth-First Search

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Q. In a weighted graph, if all edge weights are equal, which algorithm can be used instead of Dijkstra's?

A. Depth-First Search
B. Breadth-First Search
C. A* Search
D. Bellman-Ford Algorithm

Solution

If all edge weights are equal, Breadth-First Search can be used to find the shortest path, as it explores all neighbors at the present depth prior to moving on.

Correct Answer: B — Breadth-First Search

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Q. In an AVL tree, what is the balance factor of a node?

A. Height of left subtree - height of right subtree
B. Height of right subtree - height of left subtree
C. Number of nodes in left subtree - number of nodes in right subtree
D. Height of the node itself

Solution

The balance factor of a node in an AVL tree is defined as the height of the left subtree minus the height of the right subtree.

Correct Answer: A — Height of left subtree - height of right subtree

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Q. In an AVL tree, what is the maximum height difference allowed between the left and right subtrees?

A. 1
B. 2
C. 3
D. 4

Solution

An AVL tree allows a maximum height difference of 1 between the left and right subtrees.

Correct Answer: B — 2

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Q. In an AVL tree, what is the maximum height difference between the left and right subtrees of any node?

A. 0
B. 1
C. 2
D. 3

Solution

In an AVL tree, the height difference (balance factor) between the left and right subtrees of any node must be at most 1 to maintain balance.

Correct Answer: B — 1

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Q. In an AVL tree, what must be done after an insertion if the tree becomes unbalanced?

A. Perform a single rotation
B. Perform a double rotation
C. Rebuild the entire tree
D. Nothing is needed

Solution

After an insertion, if the AVL tree becomes unbalanced, a double rotation may be required to restore balance.

Correct Answer: B — Perform a double rotation

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Q. In an AVL tree, what operation is performed when a node becomes unbalanced after an insertion?

A. Rotation
B. Traversal
C. Deletion
D. Rebalancing

Solution

When a node becomes unbalanced after an insertion, a rotation (single or double) is performed to restore balance.

Correct Answer: A — Rotation

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Q. In BFS, which node is visited first?

A. The deepest node
B. The first node added to the queue
C. The last node added to the queue
D. The parent node

Solution

In BFS, the first node added to the queue is visited first, as BFS explores all neighbors at the present depth prior to moving on to nodes at the next depth level.

Correct Answer: B — The first node added to the queue

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Q. In binary search, how do you calculate the middle index?

A. (low + high) / 2
B. (low + high) / 2 + 1
C. (low + high) / 2 - 1
D. low + (high - low) / 2

Solution

The middle index is calculated using low + (high - low) / 2 to avoid overflow.

Correct Answer: D — low + (high - low) / 2

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Q. In binary search, if the target is less than the middle element, what should be the next step?

A. Search the right half
B. Search the left half
C. Return the middle element
D. Increase the middle index

Solution

If the target is less than the middle element, the next step is to search the left half of the array.

Correct Answer: B — Search the left half

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Q. In binary search, if the target value is not found, what will be the return value?

A. -1
B. 0
C. null
D. the index of the closest value

Solution

Typically, binary search returns -1 to indicate that the target value is not present in the array.

Correct Answer: A — -1

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Q. In binary search, what happens if the middle element is greater than the target?

A. Search the left half
B. Search the right half
C. Search both halves
D. Return the middle element

Solution

If the middle element is greater than the target, the search continues in the left half of the array.

Correct Answer: A — Search the left half

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Data Structures & Algorithms

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