README.md

0x19. C - Hash tables

0. >>> ht = {} mandatory

Write a function that creates a hash table.

• Prototype: hash_table_t *hash_table_create(unsigned long int size);
  • where size is the size of the array
• Returns a pointer to the newly created hash table
• If something went wrong, your function should return NULL

1. djb2 mandatory

Write a hash function implementing the djb2 algorithm.

• Prototype: unsigned long int hash_djb2(const unsigned char *str);
• You are allowed to copy and paste the function from this page

2. key -> index mandatory

Write a function that gives you the index of a key.

• Prototype: unsigned long int key_index(const unsigned char *key, unsigned long int size);
  • where key is the key
  • and size is the size of the array of the hash table
• This function should use the hash_djb2 function that you wrote earlier
• Returns the index at which the key/value pair should be stored in the array of the hash table
• You will have to use this hash function for all the next tasks

3. >>> ht['betty'] = 'holberton' mandatory

Write a function that adds an element to the hash table.

• Prototype: int hash_table_set(hash_table_t *ht, const char *key, const char *value);
  • Where ht is the hash table you want to add or update the key/value to
  • key is the key. key can not be an empty string
  • and value is the value associated with the key. value can be an empty string
• Returns: 1 if it succeeded, 0 otherwise
• In case of collision, add the new node at the beginning of the list

4. >>> ht['betty'] mandatory

Write a function that retrieves a value associated with a key.

• Prototype: char *hash_table_get(const hash_table_t *ht, const char *key);
  • where ht is the hash table you want to look into
  • and key is the key you are looking for
• Returns the value associated with the element, or NULL if key couldn’t be found

5. >>> print(ht) mandatory

Write a function that prints a hash table.

• Prototype: void hash_table_print(const hash_table_t *ht);
  • where ht is the hash table
• You should print the key/value in the order that they appear in the array of hash table
  • Order: array, list
• Format: see example
• If ht is NULL, don’t print anything

6. >>> del ht mandatory

Write a function that deletes a hash table.

• Prototype: void hash_table_delete(hash_table_t *ht);
  • where ht is the hash table

7. $ht['Betty'] = 'Holberton' #advanced

In PHP, hash tables are ordered. Wait… WAT? How is this even possible?

Before you continue, please take a moment to think about it: how you would implement it if you were asked to during an interview or a job. What data structures would you use? How would it work?

For this task, please:

• Read PHP Internals Book: HashTable
• Use the same hash function
• Use these data structures: