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Hash Tables

39 Hash Tables interview questions

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Basic Hash Table Concepts


  • 1.

    What is a Hash Table?

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  • 2.

    What is Hashing?

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  • 3.

    Explain the difference between Hashing and Hash Tables.

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  • 4.

    Provide a simple example of a Hash Function.

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  • 5.

    How do hash tables work under the hood, specifically in languages like Java, Python, and C++?

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Hash Functions and Collisions


  • 6.

    What are Hash Collisions?

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  • 7.

    Name some Collision Handling Techniques.

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  • 8.

    Describe the characteristics of a good hash function.

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  • 9.

    What is Separate Chaining, and how does it handle collisions?

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  • 10.

    Explain Open Addressing and its different probing techniques.

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Complexity and Performance


  • 11.

    Explain the Time and Space Complexity of a Hash Table.

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  • 12.

    What is a Load Factor in the context of Hash Tables?

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  • 13.

    How does the load factor affect performance in a hash table?

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  • 14.

    Discuss different ways to resize a hash table. What is the complexity involved?

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  • 15.

    How can the choice of a hash function impact the efficiency of a hash table?

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Cryptographic Hashing


  • 16.

    What is the difference between a Hash Function and a Cryptographic Hash Function?

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  • 17.

    What is the role of a Salt in Cryptographic Hashing?

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  • 18.

    Explain Types of Resistance in Cryptographic Hash Functions.

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  • 19.

    What is MD5?

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  • 20.

    What vulnerabilities exist in Hashing Algorithms like MD5 and SHA1?

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Hash Table Usage and Applications


  • 21.

    Detect if a List is Cyclic using a Hash Table.

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  • 22.

    Remove Duplicates from an Unsorted Linked List using a hash table.

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  • 23.

    Find Common Elements in two given Linked Lists and return them as a new Linked List using a hash table.

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  • 24.

    Pair socks from a pile using a Hash Table.

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  • 25.

    How can hash tables be used in caching implementations? Describe a typical use case.

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  • 26.

    Write an algorithm using a hash table to check if two strings are anagrams of each other.

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  • 27.

    Implement Autocomplete functionality using Hash Tables.

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  • 28.

    Describe how a hash table can be used in the implementation of a CDN.

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Hash Table Structures and Variants


  • 29.

    What is the difference between HashMaps and HashTables in context of Java’s data structures?

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  • 30.

    Explain Cuckoo Hashing and when it is advantageous to use.

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  • 31.

    What are Skip Lists and how do they compare to hash tables?

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  • 32.

    Discuss the concept of a Dynamic Perfect Hash Table.

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  • 33.

    In what scenarios would you use a Bloom Filter, and how does it relate to hash tables?

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Advanced Hash Table Questions


  • 34.

    What is the Pigeonhole Principle and how does it relate to hashing?

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  • 35.

    What are the advantages of Tries over Hash Tables?

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  • 36.

    Explain Robin Hood Hashing and its impact on performance and collision resolution.

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  • 37.

    What is Linear Hashing and how can it be used to handle growing datasets?

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  • 38.

    How are hash tables applied in distributed systems, for example, in consistent hashing algorithms?

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  • 39.

    Describe a situation where you would use a hash table over a binary search tree, and why.

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