Hash Table Collision Handler

Visualize hash table operations and collision resolution strategies

Configuration

Use prime numbers for better distribution

Help

What is a Hash Table?
  • A hash table stores key-value pairs using a hash function to compute array indices
  • Hash Function: Converts keys to array indices: h(key) = key % table_size
  • Ideal Performance: O(1) average time for insert, search, and delete
  • Collision: When two keys hash to the same index
  • Hash tables power dictionaries, sets, caches, and database indexing
Collision Resolution Strategies
  • Chaining: Each slot contains a linked list of all items that hash to that index
    • Pros: Simple, no limit on items, never needs resizing
    • Cons: Uses extra memory for pointers, cache unfriendly
  • Linear Probing: If slot is full, try next slot sequentially
    • Pros: Good cache locality, simple to implement
    • Cons: Primary clustering - long runs of filled slots
  • Quadratic Probing: Use quadratic function for probe sequence (i²)
    • Pros: Reduces primary clustering
    • Cons: Can miss empty slots, requires careful table size selection
Load Factor and Performance
  • Load Factor: α = n/m (items/table_size)
  • Chaining: Average chain length = α, performance degrades linearly with α
  • Open addressing: Should keep α < 0.7 for good performance
  • When α gets too high, resize table (typically double size and rehash all items)
  • Prime table sizes help distribute keys more uniformly
Hash Function Design
  • Good hash functions: Distribute keys uniformly across table
  • Simple modulo (h(k) = k % m) works for integers with prime m
  • For strings: combine character values with prime multipliers
  • Cryptographic hashes (MD5, SHA) are overkill for hash tables
  • Trade-off: Computation speed vs distribution quality
Operations Explained
  • Insert: Hash key, handle collision if needed, store key-value pair
  • Search: Hash key, follow collision resolution strategy to find key
  • Delete: Hash key, find and remove, mark slot as deleted (for probing)
  • Deleted slots in probing must be marked (not just emptied) to maintain search chains