FAQ: Hash Maps: Conceptual - Basic Hash Maps

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This community-built FAQ covers the “Basic Hash Maps” exercise from the lesson “Hash Maps: Conceptual”.

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This exercise can be found in the following Codecademy content:

Computer Science

Complex Data Structures

FAQs on the exercise Basic Hash Maps

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2

What will we do if for different keys we have same hash value ?

3 Likes
3

Can someone explain how they go from 8 -->0 , 2–>2 , 3–>3 and 5 -->1 in the text example?

                             Hash         Hash mod 4	     Release Year
People's Instinctive ...     	8	         0              	1990
The Low End Theory	            2	         2	                1991
Midnight Marauders	            3	         3	                1993
Beats, Rhymes and Life	        5	         1	                1996
4

Nevermind…

I guess I didn’t know that if there wasn’t enough to divide into a number, it would return the number.

2 /4 = 0 with remainder 2. I get it.

5

If we want to store keys and values. Can’t we just use dictionaries instead of Hash tables? I mean even dictionaries can store one value for one key and it is easier to setup.

6

8%4 = 0, 2%4 = 2, 3%4 = 3, 5%4 = 1. Hash mod 4, that’s why I think need operation % 4

1 Like
7

Yes, the hash must be taken mod (number of bins.)

8

If you mean Python dictionaries, they are implemented using hash tables already- it’s just that you don’t have to do all that bit because Python did it for you :slight_smile:

9

I think a mistake was made in this exercise. Following the hashing function of adding up the 'a’s and the 'e’s in the album title, shouldn’t the second album listed," The Low End Theory," give a hash value of 3, not 2?

The Low End Theory

10

As I was typing my question, I realized the answer. However, I wanted to post it anyway with this reply to help anyone else out that was confused by this. The hash function is literally only counting 'a’s and 'e’s. It is not counting any capital letter 'A’s and 'E’s.

7 Likes
11

What would happen if two keys generate different hash values but the modulus of their hash value (hash bucket) come out to be the same?

12

My bad… its covered in the next exercise.

1 Like
13

@bmw999 @patrickd314
this is the first exercise that I don’t understand the intructions really well. Even the question and answer is already made, concerning , I qoute : Can someone explain how they go from 8 -->0 , 2–>2 , 3–>3 and 5 –
I can figure out : Midnight Marauders 3 - 3 - 1993

I don’t get the Hash mod 3, when dividing 3/4 ? And how can I calculate 3%4 on a calculator? How to get ouput 3? I can not make a simple math out of it. May sound a bit…well anyway appreciate it to get my head simple around it…Thanks!

14

I get it, I think so ?

Midnight Marauders 3 3 1993
Beats, Rhymes and Life 5 1 1996

4/3= 1,3333’’’ = Rest 3
5/4= 1,25 = 1

15

% is used as modulo operation, and not the standard division operator. See Modulo operation - Wikipedia for details