Quadratic Hashing Explained: Definition & Use Cases | ITU Online IT Training
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Quadratic Hashing

Commonly used in Data Structures

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Quadratic hashing is a collision resolution technique used in hash tables that employs a quadratic polynomial function to determine the sequence of probe locations when a collision occurs. Instead of simply moving to the next slot, it calculates the next index based on a quadratic function of the number of attempts, helping to spread out entries more evenly and reduce clustering.

How It Works

When inserting or searching for a key in a hash table that uses quadratic hashing, the process begins by hashing the key to find an initial index. If this index is already occupied, the algorithm calculates a new index using a quadratic function, typically of the form (hash + c1 * i + c2 * i^2) modulo the table size, where i is the number of attempts made. This process continues, increasing i each time, until an empty slot is found or the key is located. The quadratic component ensures that subsequent probes are spaced out more widely than linear probing, reducing the likelihood of primary clustering.

Common Use Cases

  • Implementing hash tables where minimizing clustering improves performance.
  • Handling collisions in open addressing schemes for databases or in-memory data structures.
  • Designing hash functions for applications with high load factors to maintain efficiency.
  • Developing systems where predictable probe sequences are necessary for performance tuning.
  • Optimizing search times in hash-based caches or indexes with dynamic data.

Why It Matters

Quadratic hashing is important for IT professionals and certification candidates because it offers a more efficient collision resolution method compared to linear probing, especially in high load scenarios. Understanding this technique helps in designing robust hash tables that maintain fast access times and reduce the chances of clustering, which can degrade performance. It is particularly relevant in roles involving database management, data structure implementation, and systems optimisation, where effective data retrieval is critical for system efficiency and scalability.

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