Interview Questions and Answers
Freshers / Beginner level questions & answers
Ques 1. Find the kth to last element of a singly linked list.
Use two pointers; one moves k nodes into the list, and then both iterate until the second one reaches the end.
Example:
Input: 1 -> 2 -> 3 -> 4 -> 5, k = 2
Output: 4
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Ques 2. Remove duplicates from an unsorted linked list.
Use a hash set to keep track of unique elements while traversing the list.
Example:
Input: 1 -> 2 -> 2 -> 3 -> 4 -> 4 -> 5
Output: 1 -> 2 -> 3 -> 4 -> 5
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Ques 3. Write a function to find the middle element of a linked list.
Use two pointers; one moves one step at a time, and the other moves two steps at a time.
Example:
Input: 1 -> 2 -> 3 -> 4 -> 5
Output: 3
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Intermediate / 1 to 5 years experienced level questions & answers
Ques 4. Implement a function to reverse a singly linked list.
To reverse a linked list, you can iterate through the list and reverse the direction of pointers.
Example:
Input: 1 -> 2 -> 3 -> 4 -> 5
Output: 5 -> 4 -> 3 -> 2 -> 1
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Ques 5. Detect a cycle in a linked list.
You can use Floyd's cycle-finding algorithm, also known as the 'tortoise and hare' algorithm.
Example:
Input: 1 -> 2 -> 3 -> 4 -> 5 -> 2 (cycle)
Output: True
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Ques 6. Merge two sorted linked lists into a single sorted list.
Traverse both lists simultaneously, compare elements, and merge them into a new sorted list.
Example:
Input: List1: 1 -> 3 -> 5, List2: 2 -> 4 -> 6
Output: 1 -> 2 -> 3 -> 4 -> 5 -> 6
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Ques 7. Check if a linked list is a palindrome.
Reverse the second half of the list and compare it with the first half.
Example:
Input: 1 -> 2 -> 3 -> 2 -> 1
Output: True
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Ques 8. Swap nodes in pairs in a linked list.
Iterate through the list and swap each pair of adjacent nodes.
Example:
Input: 1 -> 2 -> 3 -> 4
Output: 2 -> 1 -> 4 -> 3
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Ques 9. Rotate a linked list by k places.
Find the length of the list, then move (length - k % length) steps to the right.
Example:
Input: 1 -> 2 -> 3 -> 4 -> 5, k = 2
Output: 4 -> 5 -> 1 -> 2 -> 3
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Ques 10. Detect the intersection point of two linked lists.
Find the lengths of both lists, move the longer list's pointer ahead, and then iterate to find the intersection.
Example:
Input: List1: 1 -> 2 -> 3, List2: 6 -> 5 -> 2 -> 3
Output: Node with value 2
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Experienced / Expert level questions & answers
Ques 11. Implement a function to add two numbers represented by linked lists.
Traverse both lists simultaneously, perform addition, and handle carry.
Example:
Input: (7 -> 2 -> 4) + (5 -> 6 -> 4)
Output: 2 -> 9 -> 8
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Ques 12. Clone a linked list with next and random pointers.
Create a copy of each node and link the copies, then separate the original and cloned lists.
Example:
Input: 1 -> 2 -> 3 -> 4
Output: 1' -> 2' -> 3' -> 4'
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Ques 13. Flatten a multilevel doubly linked list.
Use recursion to flatten each level and connect the flattened levels.
Example:
Input: 1 <-> 2 <-> 3 <-> 7 <-> 8 <-> 11 <-> 4 <-> 9 <-> 12
Output: 1 <-> 2 <-> 3 <-> 4 <-> 7 <-> 8 <-> 9 <-> 11 <-> 12
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Ques 14. Implement LRU (Least Recently Used) Cache using a linked list.
Maintain a doubly linked list to represent usage order and a hash map for quick access.
Example:
Cache capacity = 3
Operations: Get(2), Put(2, 6), Get(1), Put(1, 5), Put(1, 2)
Output: 6, 5, 2
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Ques 15. Reverse nodes in k-group in a linked list.
Reverse k nodes at a time, and connect the reversed groups.
Example:
Input: 1 -> 2 -> 3 -> 4 -> 5, k = 2
Output: 2 -> 1 -> 4 -> 3 -> 5
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