Separate Chaining

Separate Chaining

Separate chaining is a collision resolution technique used in hash tables to handle collisions. When two or more keys generate the same hash value, separate chaining ensures that all colliding keys and their associated values are stored in a separate data structure, typically a linked list or an array, within the same bucket of the hash table.

Here's how separate chaining collision resolution works:

Hash Function: A hash function is used to calculate the hash value for each key. Different keys may produce the same hash value, resulting in a collision.

Array of Buckets: The hash table is composed of an array of buckets, with each bucket associated with a specific hash index. Each bucket can hold multiple elements.

Collision Handling: When a collision occurs, the colliding elements are stored in the same bucket using a separate data structure. Typically, a linked list or an array is used to create a chain of elements within the bucket.

Insertion: To insert a key-value pair into the hash table, the hash function is applied to the key to determine the hash index. The element is then added to the corresponding bucket by appending it to the linked list or inserting it into the array.

Retrieval: To retrieve the value associated with a specific key, the hash function is again applied to the key to obtain the hash index. The bucket at that index is accessed, and a search is performed within the linked list or array to find the desired element.


Here's an example to illustrate separate chaining collision resolution:

Hash Table:

Index 0: [key1, value1] -> [key4, value4]

Index 1: [key2, value2]

Index 2: [key3, value3] -> [key5, value5] -> [key6, value6]

In this example, the hash table has three buckets. The keys key1 and key4 produce the same hash value, resulting in both elements being stored in a linked list within bucket 0. Similarly, keys key3, key5, and key6 are stored in a linked list within bucket 2.

During retrieval, the hash function is applied to the key to calculate the hash index. For example, if we want to retrieve the value associated with key5, the hash function yields index 2. We then search within the linked list in bucket 2 to find the element with key5 and retrieve its corresponding value.

Separate chaining provides an efficient and flexible way to handle collisions in hash tables. It allows for the storage of multiple elements at the same hash index without overwriting existing data. The performance of separate chaining depends on the average length of the chains and the efficiency of the search operation within the chains.

Overall, separate chaining ensures that collisions are resolved by maintaining separate data structures within the hash table, resulting in an effective and reliable method for collision resolution.