Hashing and five popular hashing functions, Data Structure & Algorithms

Q. Explain the term hashing? Explain any five well known hash functions.                        

Ans:

Hashing method provides us the direct access of record from the file dosent matter where the record is in the file. This is made possible with the help of a hashing function H which map the key with the corresponding key address. It provides us with the key- to-address transformation.

Five well known hashing functions are as follows:

The Division Method: An integer key x is divided by the table size m and the remainder is occupied as the hash value. This may be defined as

H(x)=x%m+1

Take an example, x=42 and m=13, H(42)=45%13+1=3+1=4

The Midsquare Method: In this a key is multiplied by itself and the hash value is obtained by selecting an suitable number of digits from the middle of the square. The identical positions in the square must be used for all keys. Taking an example, if the key is 12345, square of this key is given by value 152399025. If 2 digit addresses is needed then position 4th and 5th can be chosen, giving address 39.

The Folding Method: In this a key is broken into several parts. Each part has the same length similar to that of the required address apart from the last part. The parts are added together, ignoring the last carry, we get the hash address for key K.
The multiplicative method:  In this technique a real number c  such  that  0

H(x)=[m(cx%1)]+1

In this,cx%1 is the fractional part of cx and [] denotes the greatest integer less than or equal to its own contents.

The Digit Analysis: In this method the addresses is formed by selecting and shifting digits of the original key. For a given set of key, the same positions in the key and same rearrangement of the pattern must be used. By taking an example a key 7654321 is transformed to the address 1247 by selecting the digits in the position 1,2,4 and 7 then by reversing the order.

Posted Date: 7/10/2012 6:32:27 AM | Location : United States







Related Discussions:- Hashing and five popular hashing functions, Assignment Help, Ask Question on Hashing and five popular hashing functions, Get Answer, Expert's Help, Hashing and five popular hashing functions Discussions

Write discussion on Hashing and five popular hashing functions
Your posts are moderated
Related Questions
State about the Bit String Carrier set of the Bit String ADT is the set of all finite sequences of bits, including empty strings of bits, which we denote λ. This set is {λ, 0

P os t - o r d e r T r av er sal :  This can be done by both iteratively and recursively. The iterative solution would require a modification or alteration of the in-

In this sorting algorithm, multiple swapping occurs in one pass. Smaller elements move or 'bubble' up to the top of the list, so the name given to the algorithm. In this method,

Explain divide and conquer algorithms  Divide  and  conquer  is  probably  the  best  known  general  algorithm  design  method.  It   work according to the following general p

Pre-order Traversal The method of doing a pre-order traversal iteratively then has the several steps(suppose that a stack is available to hold pointers to the appropriate nodes


What do you mean by hashing? Hashing gives the direct access of record from the file no matter where the record is in the file. This is possible with the help of a hashing func

In the array implementation of lists, elements are stored into continuous locations. In order to add an element into the list at the end, we can insert it without any problem. But,

1) Which graph traversal uses a queue to hold vertices which are to be processed next ? 2) Which of the graph traversal is recursive by nature? 3) For a dense graph, Prim's a

write a pseudocode to input the top speed (in km''s/hours) of 5000 cars output the fastest speed and the slowest speed output the average (mean) speed of all the 5000 cars answers