HASHING
Presented
By:-
Radhika
MCA
5th
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Hashing Algorithms: Techniques and Collision Resolution, Slides of Design and Analysis of Algorithms
An overview of hashing algorithms, their functions, methods, and collision resolution techniques. Hashing is a technique used to store and retrieve data quickly by converting keys into hash values and using them as indices in a hash table. The direct method, division method, mid-square method, and folding method for generating hash values, as well as collision resolution techniques such as open addressing and separate chaining.
Typology: Slides
2017/2018
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HASHING
Presented
By:-
SummarySummary (^) Hashing stores the data in such a way that it can retrieved very quickly. (^) Hashing is also known as Hashing Algorithm or Message Digest Function. (^) It is a technique to convert a range of key values into a range of indexes of an array. (^) Hashing allows to update and retrieve any data entry in a constant time O(1).
Hash Table Hash Table (^) Hash table or hash map is a data structure used to store key-value pairs. (^) It is a collection of items stored to make it easy to find them later. (^) It uses a hash function to compute an index into an array.
Hash Methods Hash Methods
Direct
Method
Division
Method
Midsqu
are
Method
Folding
Method
Division Method Division Method (^) In this method, the key is divided by some integer and the remainder is taken as the index of the hash table. (^) It is also known as modulo-division method 234 431 94 7 98 1 792 Exampl e:- Assume:- Table size = 13 H(k):- 0 2 11 6 12 Remain der
Midsquare Method Midsquare Method (^) In this method, the key is squared and index of the hash table is obtained by selecting an appropriate number of digits from the middle of the square. K = 4012 K (sqr) = 16096144 H (k) = 96 Exampl e:- K = 1001 K (sqr) = 1010001 H (k) = 100
CollisionCollision (^) If ,when an element is inserted, it hashes to the same value as an already inserted element, then we have a collision and need to resolve it. (^) A method that is used to resolve the collision in hash function is called Collision Resolution.
Collision Resolution Techniques Collision Resolution Techniques Open Addressi ng Separate Chaining
Linear Probing Linear Probing (^) If the current location is used, Try the next table location. (^) Used less memory than chaining Exampl e:- 21,22, , % 5 = 21 22 11 32
1,2,1, 2
Quadratic Probing Quadratic Probing (^) Quadratic Probing operates by taking the original hash index and adding successive values of an arbitrary quadratic polynomial until an open slot is found. H (x) = (h(k) + f(i)) mod size i Exampl e:- 21,22, , % 5 = 1,2,1, 2 11 21 22 32
Advantages & Disadvantages Advantages & Disadvantages
Advantages Disadvantages
(^) Reliable method of data retrieval (^) Difficult for sequential retrieval by key. (^) More Faster (^) Inability to use duplicate keys (^) No index Storage Space required (^) Collision Occurrence (^) Time Complexity is O(1)