1. Advanced Data Structure using C++

4. Rehashing
LECTURE NOTES OF ADVANCED DATA STRUCTURE (MT-CSE 110)
Hash2 (Key) = R ‐ (Key % R) where R is a prime number smaller than the hash
table size.
If the table gets too full, the running time for the operations will start taking too
long and inserts might fail with quadratic probing.
The standard solution in this case is to build an entirely new hash table
approximately twice the size of the original, calculate a new hash value for each
key and then insert all keys into the new table (then destroying the old table).
This is known as reorganization or rehashing.
HASHING ALGORITHMS
Hashing is a technique in which a given key field value is converted in to address
of a storage location of the record by applying some operations on it.This
technique is very useful for creatingand using random file organisation.
A number of hash techniques are available.some examples of hashing
algorithms are as follows:
1. Method of division:In this method the key field value is divided by some
suitable number (a prime number) so that quotient can be used as the
address of the record.e.g.key field value 210 can be divided by 13 to
obtain quotient 16 as address of the record.
2. Division/Remainder Method:In this method key field value is divided by
appropriate integer and the remainder is used as the relative address
for the record. e.g. a file having 90 records with primary key values
between 300 to 5000.let the divisor be 97.Then if the key values are
600,1082,1540,the remainder after divison by 97 are 18,15 and 85
respectively.common practice is to add 1 to the remainder.hence relative
address are 19,16 & 86 respectively.
Prepared By :­
Er. Harvinder Singh
Assist Prof., CSE, H.C.T.M (Kaithal) Page ‐ 27 ‐