Mphasis Hash Table and Heap Quiz 1

The sequence (A) doesn’t create the hash table as the element 52 appears before 23 in this sequence.

The sequence (B) doesn’t create the hash table as the element 33 appears before 46 in this sequence.

The sequence (C) creates the hash table as 42, 23 and 34 appear before 52 and 33, and 46 appears before 33.

The sequence (D) doesn’t create the hash table as the element 33 appears before 23 in this sequence.

A hash function is a function that takes a set of inputs of any arbitrary size and fits them into a table or other data structure that contains fixed-size elements. The table or data structure generated is usually called a hash table.

Since every key has a unique array position, searching takes a constant time

Making the hash function random is not really a good choice, although it is considered one of the techniques to avoid collisions along with chaining and simple uniform hashing.

Chaining is the best

For each entry probability of collision is 1/20 {as possible total spaces =20, and an entry will go into only 1 place}
Say after inserting x values probability becomes ½
(1/20).x = ½
X=10

The key is hashed twice; first by hashCode() of Object class and then by internal hashing method of HashMap class.

Hashmap outputs in the order of hashcode of the keys. So it is unordered but will always have same result for same set of keys.

Collection interface provides add, remove, search or iterate while map has clear, get, put, remove, etc.
Map interface is the HashMap. It is a hash table based implementation of the Map interface. It implements all of the Map operations and allows null values and one null key. Also, this class does not maintain any order among its elements.

Vector implements AbstractList which internally implements Collection. Others come from implementing the Map interface.

IdentityHashMap is rarely used as it violates the basic contract of implementing equals() and hashcode() method.