Hash

Question 1

When adding all elements from an array to a hash? Why can’t you use the hash.addAll function?

Answer 1

Because it treats the primitive array as one big object. To add everything from an array to a hash, you must use a typical for loop iterator.

Question 2

Why use a HashSet over a linked list?

Answer 2

-Linked List have a slow lookup/search
- arrays don’t have random access so accessing an element takes O(n)

Question 3

Why use a boolean array?

Answer 3

We use a boolean array as a hashset that marks if we’ve seen that value before.

Question 4

What does the Hash do to a String?

Answer 4

Returns an integer

For example, if we use “Nick” it might return 4 to represent the length of the name

Then we pass it to the 4th spot

Question 5

Hash Function

Answer 5

A function that takes an input and retunrs an integer based on that input’s value

Question 6

Hash Code

Answer 6

The value returned by a Hash Function that determines the numeric mapping of this element

Question 7

HashSet

Answer 7

A data structure in which elements are placed in their respective array locations based on their hash code

Question 8

HashSet Add

Answer 8

O(1)

Question 9

HashSet Remove

Answer 9

O(1)

Question 10

HashSet Contains

Answer 10

O(1)

Question 11

How to deal with collisions in a hashset?

Answer 11

• ## Open Addressing: Just put it in the empty spot

Question 12

How does contains work in a hashset?

Answer 12

• Get the location through the same hash method and see if its there

Question 13

What if the contains can’t find it in our hashset?

Answer 13

• Get the location, if we don’t see it, keep going through the list until we find it or if we find a null, then return false because then its impossible to be in our hashset