Hashing Techniques Quiz

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Questions and Answers

In Cuckoo Hashing, what happens when a key is pushed out of its current location?

  • The key is lost forever
  • The key is inserted into its alternative location (correct)
  • The key is hashed again
  • The key triggers relocations in cascade

Which operation in Cuckoo Hashing has an expected O(1) time complexity?

  • Rebuilding the hash table
  • Search
  • Delete
  • Insert (correct)

What strategy is used to maintain a dynamic set of buckets in Extendible Hashing?

  • Consistent Hashing
  • Radix search tree
  • Trie organization (correct)
  • Linear Probing

What triggers other relocations in cascade in Cuckoo Hashing?

<p>Pushing a key into its alternative location (C)</p> Signup and view all the answers

Which type of hashing scheme is known for being typically 20-30% slower than linear probing?

<p>Cuckoo Hashing (C)</p> Signup and view all the answers

What action leads to the hash table being rebuilt with new hash functions in Cuckoo Hashing?

<p>Creating a cycle due to relocations (D)</p> Signup and view all the answers

Which technique is used to solve collisions in Java 8 HashMap?

<p>Chaining (D)</p> Signup and view all the answers

What is the hash function used in Java 8 HashMap for calculating hash values?

<p>static final int hash(Object key) { ... } (C)</p> Signup and view all the answers

In Java 10 HashMap, when does the resizing of the table occur?

<p>When load factor exceeded (C)</p> Signup and view all the answers

What happens in Linear Probing if the bucket for insertion is already occupied?

<p>Insertion in the next available bucket (C)</p> Signup and view all the answers

How are deletions handled in Linear Probing?

<p>Shift next cells in cascade if needed (A)</p> Signup and view all the answers

What strategy does Java 8 HashMap use when a bin gets overpopulated?

<p>Switch its content to a Tree (B)</p> Signup and view all the answers

What is the main difference between Quadratic Probing and Linear Probing?

<p>Quadratic Probing modifies the initial index based on a quadratic formula, while Linear Probing increments the index linearly. (A)</p> Signup and view all the answers

What condition must be satisfied for Linear Probing to guarantee O(1) expected time complexity?

<p>Ensuring the load factor is not too high (A)</p> Signup and view all the answers

In Python 2.7 dictionaries, how is collision resolved when using probing?

<p>Utilizing a pseudo-random probing sequence (B)</p> Signup and view all the answers

What is the purpose of resizing the hash table in Python 2.7 dictionaries?

<p>To maintain a specific load factor (D)</p> Signup and view all the answers

Why does Python 2.7 use the low order bits of the key's hash for the initial index?

<p>For fast computation with good locality (A)</p> Signup and view all the answers

What makes Quadratic Probing slower than Linear Probing in practice?

<p>The quadratic increase in probe positions (C)</p> Signup and view all the answers

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Study Notes

Cuckoo Hashing

  • When a key is pushed out of its current location, it triggers other relocations in a cascade.
  • The search operation has an expected O(1) time complexity.
  • If an element is pushed out of its current location, the hash table is rebuilt with new hash functions.

Extendible Hashing

  • A dynamic set of buckets is maintained using a strategy where buckets can be split or merged based on the load factor.

Hashing Schemes

  • Cuckoo Hashing is a type of hashing scheme that is typically 20-30% slower than linear probing.

Java 8 HashMap

  • Collisions are solved using a technique called chaining, where a linked list is used to store colliding elements.
  • The hash function used to calculate hash values is the built-in hashCode() method.
  • When a bin gets overpopulated, Java 8 HashMap uses a strategy called treeification, where the bin is converted into a balanced tree.

Java 10 HashMap

  • The resizing of the table occurs when the load factor exceeds a certain threshold.

Linear Probing

  • If the bucket for insertion is already occupied, the algorithm probes subsequent buckets until an empty bucket is found.
  • Deletions are handled by marking the bucket as deleted, but not actually removing the element.
  • The main difference between Quadratic Probing and Linear Probing is the probing sequence used to find an empty bucket.
  • For Linear Probing to guarantee O(1) expected time complexity, the load factor must be less than 0.5.

Python 2.7 Dictionaries

  • Collisions are resolved using linear probing.
  • The purpose of resizing the hash table is to maintain a good load factor and prevent collisions.
  • The low order bits of the key's hash are used for the initial index to minimize collisions.
  • Quadratic Probing is slower than Linear Probing in practice because it has a higher chance of clustering, leading to more collisions.

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