Laboratory: Hash Tables

Summary:

Prerequisites: Familiarity with structs and pointers. Familiarity with the dictionary data type.

• Preparation
• Exercises
  • Exercise 1: Overlaps
  • Exercise 2: Dumping the Table
  • Exercise 3: Finding Keys by Value
• For Those With Extra Time

Preparation

a. Create a new directory for this lab. I'd suggest Labs/Hashtables, but you can choose whatever you'd like.

b. Copy the code from Examples/Hashtables.

c. Review the code to ensure that you understand what's happening.

Exercises

Exercise 1: Overlaps

a. Find two keys that give the same index in a size 20 hash table.

b. Add a unit test to verify that the hash table performs correctly if we use both of those keys. In particular, you should verify that if both keys have different values, they retrieve the different values.

Exercise 2: Dumping the Table

Write a procedure, dump (hashtable *table), that prints all of the key/value pairs in the table.

Note: You can't easily unit test this procedure, so you may just want to add a dump at the end of your unit tests.

Exercise 3: Finding Keys by Value

Traditionally, we use a hash table to look up values by key. But we could try the reverse, too. Write a function, char *find_key (hashtable *table, char *value), that returns one key that maps to value. If no such key exists, return null.

For Those With Extra Time

Sketch an algorithm for deleting a key from the hash table.