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1
Which algorithm detects a cycle in a singly linked list using two pointers in O(N) time and O(1) auxiliary space?
A.
Floyd's Cycle-Finding Algorithm (Tortoise and Hare)
B.
Dijkstra's Shortest Path Algorithm
C.
Kadane's Algorithm
D.
Boyer-Moore Voting Algorithm
Explanation & Key
Correct Answer:
2
How do you find the starting node of a cycle in a singly linked list after slow and fast pointers meet at node P?
A.
Reset slow pointer to head and move fast pointer backwards
B.
Reset fast pointer to head and move both slow and fast by 1 step until they meet
C.
Count the cycle length and divide by 2
D.
Delete all nodes visited so far
Explanation & Key
Correct Answer:
3
What is the time complexity to find the middle element of a singly linked list in a single pass?
A.
O(N^2)
B.
O(log N)
C.
O(N)
D.
O(1)
Explanation & Key
Correct Answer:
4
How can you reverse a singly linked list iteratively in O(N) time and O(1) space?
A.
Using a recursion stack of depth N
B.
Using a hash map storing node values
C.
By swapping node values across the list
D.
Using three pointers: prev, curr, and next
Explanation & Key
Correct Answer:
5
What is the primary memory disadvantage of a Singly Linked List compared to an Array?
A.
Extra memory overhead per node for storing pointers and loss of cache locality
B.
Fixed capacity that cannot grow dynamically
C.
Inability to store string or object data types
D.
Excessive fragmentation caused by contiguous memory blocks
Explanation & Key
Correct Answer:
6
What is the time complexity to insert an element at the beginning of a singly linked list?
A.
O(N)
B.
O(1)
C.
O(log N)
D.
O(N^2)
Explanation & Key
Correct Answer:
7
How can you delete a node from a singly linked list in O(1) time if you are ONLY given a pointer to that node (not the head) and it is not the last node?
A.
Traverse backward using pointer arithmetic
B.
Set node = NULL directly
C.
Copy the value of node->next into node, then delete node->next
D.
It is theoretically impossible in singly linked lists
Explanation & Key
Correct Answer:
8
What data structure combination is used to implement an LRU (Least Recently Used) Cache with O(1) get and put operations?
A.
Binary Search Tree and Queue
B.
Stack and Dynamic Array
C.
Max-Heap and Trie
D.
Doubly Linked List and Hash Map
Explanation & Key
Correct Answer:
9
How can you find the intersection point of two singly linked lists of lengths M and N in O(M + N) time and O(1) space?
A.
Calculate lengths diff D, advance longer list by D, then traverse together
B.
Sort both linked lists first
C.
Use a two-dimensional matrix of node pointers
D.
Apply binary search on the addresses
Explanation & Key
Correct Answer:
10
What is the advantage of using a Dummy (Sentinel) Head node when working with linked lists?
A.
It halves the time complexity of all operations
B.
It simplifies boundary edge cases like inserting or deleting at the head without special-case branching
C.
It converts singly linked list into doubly linked list automatically
D.
It enables random access by index in O(1) time
Explanation & Key
Correct Answer:
11
In a circular singly linked list, what does the `next` pointer of the last node point to?
A.
NULL / nullptr
B.
Middle node of the list
C.
Head node of the list
D.
Itself
Explanation & Key
Correct Answer:
12
What is the time complexity to find the K-th node from the end of a singly linked list in a single pass?
A.
O(K * N)
B.
O(N log N)
C.
O(K^2)
D.
O(N)
Explanation & Key
Correct Answer:
13
What is a Skip List and what is its average search complexity?
A.
A probabilistic multi-level linked list with average O(log N) search time
B.
A linked list that skips odd-indexed elements with O(N) search time
C.
A doubly linked list that uses XOR pointer representation
D.
A cache-friendly B-tree variant
Explanation & Key
Correct Answer:
14
How does an XOR Linked List (Memory Efficient Doubly Linked List) store prev and next pointers in a single field?
A.
By multiplying the memory addresses
B.
By storing XOR of addresses: `npx = address(prev) ^ address(next)`
C.
By hashing node contents into a 32-bit integer
D.
By alternating pointers on odd and even nodes
Explanation & Key
Correct Answer:
15
How do you check if a singly linked list is a palindrome in O(N) time and O(1) auxiliary space?
A.
Store node values in an auxiliary stack of size N
B.
Construct an adjacency list and run BFS
C.
Find the middle node, reverse the second half, and compare both halves
D.
Convert the linked list into a circular queue
Explanation & Key
Correct Answer:
16
What is the time complexity of merging K sorted linked lists having a total of N nodes using a Min-Heap?
A.
O(N * K)
B.
O(K log N)
C.
O(N^2)
D.
O(N log K)
Explanation & Key
Correct Answer:
17
What happens if you delete a node in C++ using `delete node;` without updating the previous node's `next` pointer?
A.
A dangling pointer is created, leading to undefined behavior or segmentation fault on access
B.
The compiler automatically fixes the link
C.
The operating system prevents the program from compiling
D.
The linked list converts into an array
Explanation & Key
Correct Answer:
18
In a Doubly Linked List, how many pointer updates are required to insert a node between two existing nodes?
A.
2
B.
4
C.
6
D.
1
Explanation & Key
Correct Answer:
19
What is the optimal approach to remove duplicates from an unsorted singly linked list in O(N) time?
A.
Use two nested loops comparing every pair in O(N^2)
B.
Sort the list using QuickSort in O(N log N)
C.
Use a Hash Set to track seen values while traversing
D.
Reverse the linked list twice
Explanation & Key
Correct Answer:
20
What is the effect of unrolling in an Unrolled Linked List?
A.
It removes all pointers entirely
B.
It converts the list into a balanced AVL tree
C.
It stores elements in reverse sequential order
D.
Each node stores an array of elements, improving cache locality and reducing pointer overhead
Explanation & Key
Correct Answer:
21
How can you clone a linked list with next and random pointers in O(N) time and O(1) auxiliary space?
A.
Interweave cloned nodes between original nodes (`orig->next = clone`), copy random pointers, then separate lists
B.
Use a 2D adjacency matrix of size N x N
C.
Use a double recursion tree without base cases
D.
Sort nodes based on their memory addresses
Explanation & Key
Correct Answer:
22
What is the time complexity of deleting the last node in a Singly Linked List of length N (with head pointer only)?
A.
O(1)
B.
O(N)
C.
O(log N)
D.
O(N^2)
Explanation & Key
Correct Answer:
23
What is the time complexity of deleting the tail node in a Doubly Linked List with a tail pointer?
A.
O(N)
B.
O(log N)
C.
O(1)
D.
O(N^2)
Explanation & Key
Correct Answer:
24
How can you reorder a linked list L0 -> L1 -> ... -> Ln-1 -> Ln to L0 -> Ln -> L1 -> Ln-1 -> ... in O(N) time?
A.
Bubble sort the list by target indices
B.
Convert list to adjacency list and perform topological sort
C.
Use a 3-way partition around median
D.
Find middle, reverse second half, and merge two halves alternately
Explanation & Key
Correct Answer:
25
What causes memory leak in linked list operations in C/C++?
A.
Failing to `free()` or `delete` removed nodes from the heap
B.
Using recursion to traverse nodes
C.
Allocating the dummy head node on the stack
D.
Using pointer comparisons with NULL
Explanation & Key
Correct Answer:
26
How do you find the middle element of a singly linked list in a single pass?
A.
Count nodes first then traverse n/2
B.
Two pointers: advance slow by 1 node and fast by 2 nodes; when fast reaches end, slow is at the middle
C.
Store all node values in a binary tree
D.
Use a reverse pointer
Explanation & Key
Correct Answer:
27
What is the time complexity of merging two sorted singly linked lists of lengths m and n into a single sorted list?
A.
O(m * n)
B.
O(m + n)
C.
O(log(m + n))
D.
O(m log n)
Explanation & Key
Correct Answer:
28
In a Doubly Linked List, what is the time complexity of deleting a given node if a pointer to that node is already provided?
A.
O(n)
B.
O(1)
C.
O(log n)
D.
O(n^2)
Explanation & Key
Correct Answer:
29
How can you delete a node in a singly linked list given only a pointer to that node (not the head) in O(1) time, assuming it is not the tail?
A.
Traverse backward using virtual memory pointers
B.
Copy the value of node->next into node, then delete node->next by setting node->next = node->next->next
C.
It is mathematically impossible
D.
Convert the list to a circular list
Explanation & Key
Correct Answer:
30
What is the primary advantage of a Sentinel (Dummy) Head Node in linked list implementations?
A.
It speeds up pointer dereference at the hardware level
B.
It eliminates special edge case handling for operations at the head of the list (e.g. insertions/deletions at position 0)
C.
It reduces the space complexity of the list to O(1)
D.
It turns a singly linked list into a doubly linked list
Explanation & Key
Correct Answer:
31
In a Circular Singly Linked List of size n, what is the condition indicating you have traversed back to the start node?
A.
curr == nullptr
B.
curr->next == head
C.
curr->val == 0
D.
curr == head->next
Explanation & Key
Correct Answer:
32
What is the space overhead of a pointer in a 64-bit operating system for each node in a linked list?
A.
2 bytes
B.
4 bytes
C.
8 bytes
D.
16 bytes
Explanation & Key
Correct Answer:
33
How can you detect the intersection node of two singly linked lists of lengths L1 and L2 in O(L1 + L2) time and O(1) space?
A.
Store all addresses of List 1 in a hash set
B.
Advance two pointers simultaneously; when either pointer reaches null, redirect it to the head of the other list; they collide at the intersection
C.
Reverse both lists simultaneously
D.
Binary search over memory addresses
Explanation & Key
Correct Answer:
34
What is the time complexity to reorder a linked list to L0 -> Ln -> L1 -> Ln-1 -> L2 -> Ln-2 ... in O(1) extra space?
A.
O(n^2)
B.
O(n log n)
C.
O(n)
D.
O(1)
Explanation & Key
Correct Answer:
35
Why does an array exhibit significantly better cache locality than a linked list during sequential traversal?
A.
Arrays have fewer elements than linked lists
B.
Array elements reside in contiguous memory, allowing CPU cache line prefetching (spatial locality)
C.
Linked list nodes are always allocated in CPU registers
D.
Pointers bypass the CPU cache entirely
Explanation & Key
Correct Answer:
36
What is a Skip List data structure?
A.
A linked list that skips all even numbers
B.
A probabilistic multi-level linked list that supports O(log n) search, insertion, and deletion
C.
A doubly linked list with no tail pointer
D.
An array backed by a linked list
Explanation & Key
Correct Answer:
37
How do you remove the N-th node from the end of a singly linked list in a single traversal pass?
A.
Advance first pointer by N steps; then advance first and second pointers together until first reaches the end; second pointer is at the node before target
B.
Reverse the list, delete the N-th node, then reverse it back
C.
Use a hash map of node indices
D.
Traverse backward from the tail
Explanation & Key
Correct Answer:
38
In an XOR Linked List (Memory-Efficient Doubly Linked List), how is the pointer field calculated?
A.
pointer = prev + next
B.
pointer = prev XOR next (bitwise exclusive OR of memory addresses)
C.
pointer = prev AND next
D.
pointer = prev * next
Explanation & Key
Correct Answer:
39
What happens if you delete a node in C++ using `delete node;` without first updating its predecessor's `next` pointer?
A.
Compilation error
B.
A dangling pointer is created in the predecessor, leading to undefined behavior or crash when dereferenced
C.
The operating system automatically updates the predecessor pointer
D.
The predecessor node is also deleted automatically
Explanation & Key
Correct Answer:
40
Which operation is O(1) in a Doubly Linked List with head and tail pointers, but O(n) in a Singly Linked List with head and tail pointers?
A.
Insert at head
B.
Delete from head
C.
Insert at tail
D.
Delete from tail
Explanation & Key
Correct Answer:
41
What is the time complexity to check whether a singly linked list of size n is a palindrome in O(1) auxiliary space?
A.
O(n^2)
B.
O(n log n)
C.
O(n)
D.
O(log n)
Explanation & Key
Correct Answer:
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