Data Structures Interview Questions and Answers for 7 years experience

1. What are the differences between arrays and linked lists?

   • Answer: Arrays store elements contiguously in memory, offering fast access via index but limited resizing. Linked lists store elements in nodes with pointers to the next node, allowing dynamic resizing but slower access requiring traversal. Arrays are generally more efficient for random access, while linked lists are better for frequent insertions and deletions.

2. Explain the concept of a binary search tree (BST).

   • Answer: A BST is a tree data structure where each node has at most two children, referred to as the left and right child. The left subtree contains nodes with keys less than the node's key, and the right subtree contains nodes with keys greater than the node's key. This property allows for efficient searching, insertion, and deletion in O(log n) time on average.

3. How do you handle collisions in hash tables?

   • Answer: Collisions occur when two keys hash to the same index. Common collision resolution techniques include separate chaining (storing colliding elements in a linked list at the index) and open addressing (probing for the next available slot). The choice depends on factors like expected load factor and performance requirements.

4. Describe different types of linked lists.

   • Answer: Common types include singly linked lists (each node points to the next), doubly linked lists (each node points to the next and previous), circular linked lists (the last node points back to the first), and circular doubly linked lists (combining circular and doubly linked properties).

5. What is a heap data structure? Explain min-heap and max-heap.

   • Answer: A heap is a tree-based data structure that satisfies the heap property: the value of each node is greater than or equal to (for a max-heap) or less than or equal to (for a min-heap) the value of its children. Min-heaps prioritize the smallest element, while max-heaps prioritize the largest. They are commonly implemented using arrays for efficiency.

6. Explain the concept of a graph and its different representations.

   • Answer: A graph is a collection of nodes (vertices) and edges connecting them. Representations include adjacency matrices (a 2D array indicating connections) and adjacency lists (an array of lists representing connections for each node). The choice depends on the graph's density and the operations to be performed.

7. What are different graph traversal algorithms?

   • Answer: Breadth-first search (BFS) explores nodes level by level, while depth-first search (DFS) explores as far as possible along each branch before backtracking. Both are fundamental for various graph algorithms.

8. Describe Dijkstra's algorithm.

   • Answer: Dijkstra's algorithm finds the shortest path from a single source node to all other nodes in a weighted graph with non-negative edge weights. It uses a priority queue to efficiently select the node with the smallest distance.

9. Explain the concept of a Trie.

   • Answer: A Trie (prefix tree) is a tree-like data structure used for efficient retrieval of strings. Each node represents a character, and paths from the root to a node represent prefixes of strings. Tries are useful for autocompletion and spell checking.

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