Week 4: Programming Assignments (8 points)

Programming Assignments: Hashing

Both assignments are related to fixed sized hash tables. The hash tables store string (str) values. The hash value (slot) is calculated with the following hash function for strings:

procedure hash(data):
    sum = 0
    for i = 0 to N-1 do
        sum += ascii(data[i])
    return sum % X

where N is the length of the string (data), % is the symbol for the mod operation and X is a parameter of the hash table. The ascii value of a character can be calculated with the function ord in Python.

Assignment 4.1: Linear Probing (4 points)

Implement a fixed sized hash table in Python that uses linear probing for collision resolution. Create a class HashLinear which has the table size \(M\) as a input value when a object is created. The class has following methods:

insert(data: str): inserts new data into the hash table, no duplicates
delete(data: str): removes data from the hash table
print(): prints the content of the hash table (the data string in each slot separated with a space; skip empty slots; see the example below)

For hashing use \(X = M\).

A code template with an example program (the hash table has the size of \(M=8\)):

class HashLinear:
    # TODO


if __name__ == "__main__":
    table = HashLinear(8)
    table.insert("BM40A1500")
    table.insert("fOo")
    table.insert("123")
    table.insert("Bar1")
    table.insert("10aaaa1")
    table.insert("BM40A1500")
    table.print()   # 10aaaa1 BM40A1500 fOo 123 Bar1
    table.delete("fOo")
    table.delete("Some arbitary string which is not in the table")
    table.delete("123")
    table.print()   # 10aaaa1 BM40A1500 Bar1

Submit your solution in CodeGrade as hashlinear.py.

Assignment 4.1: Bucket Hashing (4 points)

Implement a fixed sized hash table in Python that uses bucket hashing for collision resolution. Create a class HashBucket which has the table size \(M\) and number of equal sized buckets \(B\) as the input values when a object is created. The hash table has a overflow array of size \(M\). The class has the following methods:

insert(data): inserts new data in the hash table, no duplicates
delete(data): removes data from the hash table
print(): prints the content of the hash table and the overflow array (the data string in each slot followed by the data in the overflow array; slots separated with a space and empty slots skipped; see the example below)

For hashing use \(X = B\). Filling the buckets starts from the top and overflow values are appended to the end of the overflow array.

A code template with an example program (the hash table has the size of \(M=8\) and has \(B=4\) buckets):

class HashBucket:
    # TODO


if __name__ == "__main__":
    table = HashBucket(8, 4)
    table.insert("BM40A1500")
    table.insert("fOo")
    table.insert("123")
    table.insert("Bar1")
    table.insert("10aaaa1")
    table.insert("BM40A1500")
    table.print()   # fOo BM40A1500 123 Bar1 10aaaa1
    table.delete("fOo")
    table.delete("Some arbitary string which is not in the table")
    table.delete("123")
    table.print()   # BM40A1500 Bar1 10aaaa1

Submit your solution in CodeGrade as hashbucket.py.