hash_map_oa.py

# Name: Kristin Eberman
# OSU Email: ebermank@oregonstate.edu
# Course: CS261 - Data Structures (section 404)
# Assignment: 6 - HashMap Implementation - Open Addressing
# Due Date: December 2, 2022
# Description: This assignment implements 10 methods within the HashMap class
#       using a DynamicArray to store the hash table and implements
#       Open Addressing with Quadratic Probing for collision resolution

from a6_include import (DynamicArray, DynamicArrayException, HashEntry,
                        hash_function_1, hash_function_2)


class HashMap:
    def __init__(self, capacity: int, function) -> None:
        """
        Initialize new HashMap that uses
        quadratic probing for collision resolution
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        self._buckets = DynamicArray()

        # capacity must be a prime number
        self._capacity = self._next_prime(capacity)
        for _ in range(self._capacity):
            self._buckets.append(None)

        self._hash_function = function
        self._size = 0

    def __str__(self) -> str:
        """
        Override string method to provide more readable output
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        out = ''
        for i in range(self._buckets.length()):
            out += str(i) + ': ' + str(self._buckets[i]) + '\n'
        return out

    def _next_prime(self, capacity: int) -> int:
        """
        Increment from given number to find the closest prime number
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        if capacity % 2 == 0:
            capacity += 1

        while not self._is_prime(capacity):
            capacity += 2

        return capacity

    @staticmethod
    def _is_prime(capacity: int) -> bool:
        """
        Determine if given integer is a prime number and return boolean
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        if capacity == 2 or capacity == 3:
            return True

        if capacity == 1 or capacity % 2 == 0:
            return False

        factor = 3
        while factor ** 2 <= capacity:
            if capacity % factor == 0:
                return False
            factor += 2

        return True

    def get_size(self) -> int:
        """
        Return size of map
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        return self._size

    def get_capacity(self) -> int:
        """
        Return capacity of map
        DO NOT CHANGE THIS METHOD IN ANY WAY
        """
        return self._capacity

    # ------------------------------------------------------------------ #

    def put(self, key: str, value: object) -> None:
        """
         Adds or updates a key/value pair in the hash map
         :param key: Unique key associated with value
         :param value: Value associated with key
         :return: None
         """
        # Resize the array if load factor >= 0.5
        if self.table_load() >= 0.5:
            self.resize_table(self._capacity * 2)

        # Use hash function to generate hash value and associated index
        hash = self._hash_function(key)
        index = hash % self._capacity

        # Initialize new HashEntry
        new_entry = HashEntry(key, value)

        # Initialize boolean to control loop & quadratic probing variables
        filled = False
        probe_count = 1
        probe_index = index

        while not filled:
            # If index is empty, fill with new_entry
            if not self._buckets[probe_index]:
                self._buckets[probe_index] = new_entry
                self._size += 1
                filled = True

            # If array element is a tombstone, overwrite it
            elif self._buckets[probe_index].is_tombstone:
                self._buckets[probe_index] = new_entry
                self._size += 1
                filled = True

            # If key already exists, update its value (do not increment size)
            elif self._buckets[probe_index].key == key:
                self._buckets[probe_index].value = value
                filled = True

            # Use quadratic probing formula to find next possible index
            else:
                probe_index = (index + probe_count ** 2) % self._capacity
                probe_count += 1

    def table_load(self) -> float:
        """
        Returns the current hash table load factor
        :return: Number of elements (size) / number of buckets (capacity)
        """
        return self._size / self._capacity

    def empty_buckets(self) -> int:
        """
        Returns the number of empty buckets in the hash table
        :return: Integer value that represents number of empty buckets
        """
        # Empty buckets = the array's capacity minus size of HashMap
        return self._capacity - self._size

    def resize_table(self, new_capacity: int) -> None:
        """
        Changes capacity of the hash table; rehashes all key/value pairs
        :param new_capacity: New value for capacity of underlying array
        :return: None
        """
        # Don't resize if new_capacity < current number of elements
        if new_capacity < self._size:
            return

        # Initialize HashMap with new capacity
        resized_hash = HashMap(new_capacity, self._hash_function)

        # Iterate over all elements in the original array
        for i in range(self._capacity):
            # Only re-hash elements that exist and are not tombstone values
            if self._buckets[i] and not self._buckets[i].is_tombstone:
                resized_hash.put(self._buckets[i].key, self._buckets[i].value)

        # Update/re-point the original buckets and capacity variables
        self._capacity = resized_hash._capacity
        self._buckets = resized_hash._buckets

    def get(self, key: str) -> object:
        """
        Returns the value associated with a given key
        :param key: Key to search for in the HashMap
        :return: Value of given key if it exists, otherwise None
        """
        # Use hash function to find index of key & set up probing variables
        hash = self._hash_function(key)
        index = hash % self._capacity
        probe_count = 1
        probe_index = index

        # Iterate over array to search for key value
        while self._buckets[probe_index]:
            if self._buckets[probe_index].key == key and not self._buckets[probe_index].is_tombstone:
                return self._buckets[probe_index].value
            else:
                # Use quadratic probing formula to find next possible index
                probe_index = (index + probe_count ** 2) % self._capacity
                probe_count += 1

        # If the key is not found, return None
        return None

    def contains_key(self, key: str) -> bool:
        """
        Searches for a given key within the HashMap (using get method)
        :param key: Key to search for
        :return: True if the key is found, otherwise False
        """
        if self.get(key) is None:
            return False
        return True

    def remove(self, key: str) -> None:
        """
        Removes key/value pair if key exists in the HashMap
        :param key: Key to search for and remove
        :return: None
        """
        # Use hash function to find index of key & set up probing variables
        hash = self._hash_function(key)
        index = hash % self._capacity
        probe_count = 1
        probe_index = index

        # Iterate over array to search for key value
        while self._buckets[probe_index]:
            if self._buckets[probe_index].key == key and not self._buckets[probe_index].is_tombstone:
                # If key is found, set tombstone to True and decrement size
                self._buckets[probe_index].is_tombstone = True
                self._size -= 1
            else:
                # Use quadratic probing formula to find next possible index
                probe_index = (index + probe_count ** 2) % self._capacity
                probe_count += 1

    def clear(self) -> None:
        """
        Clears the contents of the HashMap without changing its capacity
        :return: None
        """
        # Override _buckets with an empty DynamicArray and reset size to 0
        self._buckets = DynamicArray()
        for _ in range(self._capacity):
            self._buckets.append(None)
        self._size = 0

    def get_keys_and_values(self) -> DynamicArray:
        """
        Creates a dynamic array that contains tuples of all key/value pairs
        stored in the HashMap
        :return: Dynamic array of key/value tuples
        """
        # Initialize an empty dynamic array to fill with tuples
        key_value_arr = DynamicArray()

        # Iterate over the HashMap
        for i in range(self._capacity):
            # Only add tuples for existing elements that are not tombstones
            if self._buckets[i] and not self._buckets[i].is_tombstone:
                key_value_arr.append((self._buckets[i].key, self._buckets[i].value))
        return key_value_arr

    def __iter__(self):
        """
        Method enables the HashMap to iterate across itself
        :return: None
        """
        # Initialize index variable to track progress of iterator
        self._index = 0
        return self

    def __next__(self):
        """
        Returns value of the next active element in the HashMap based on the
        current iterator location, then increments index/iterator position
        """
        try:
            element = self._buckets.get_at_index(self._index)
            self._index += 1

            # Skip elements that are empty or are tombstones
            while not element or element.is_tombstone:
                element = self._buckets.get_at_index(self._index)
                self._index += 1

        # StopIteration exception is raised when there are no more items
        except DynamicArrayException:
            raise StopIteration

        return element


# ------------------- BASIC TESTING ---------------------------------------- #

if __name__ == "__main__":

    print("\nPDF - put example 1")
    print("-------------------")
    m = HashMap(53, hash_function_1)
    for i in range(150):
        m.put('str' + str(i), i * 100)
        if i % 25 == 24:
            print(m.empty_buckets(), round(m.table_load(), 2), m.get_size(), m.get_capacity())

    print("\nPDF - put example 2")
    print("-------------------")
    m = HashMap(41, hash_function_2)
    for i in range(50):
        m.put('str' + str(i // 3), i * 100)
        if i % 10 == 9:
            print(m.empty_buckets(), round(m.table_load(), 2), m.get_size(), m.get_capacity())

    print("\nPDF - table_load example 1")
    print("--------------------------")
    m = HashMap(101, hash_function_1)
    print(round(m.table_load(), 2))
    m.put('key1', 10)
    print(round(m.table_load(), 2))
    m.put('key2', 20)
    print(round(m.table_load(), 2))
    m.put('key1', 30)
    print(round(m.table_load(), 2))

    print("\nPDF - table_load example 2")
    print("--------------------------")
    m = HashMap(53, hash_function_1)
    for i in range(50):
        m.put('key' + str(i), i * 100)
        if i % 10 == 0:
            print(round(m.table_load(), 2), m.get_size(), m.get_capacity())

    print("\nPDF - empty_buckets example 1")
    print("-----------------------------")
    m = HashMap(101, hash_function_1)
    print(m.empty_buckets(), m.get_size(), m.get_capacity())
    m.put('key1', 10)
    print(m.empty_buckets(), m.get_size(), m.get_capacity())
    m.put('key2', 20)
    print(m.empty_buckets(), m.get_size(), m.get_capacity())
    m.put('key1', 30)
    print(m.empty_buckets(), m.get_size(), m.get_capacity())
    m.put('key4', 40)
    print(m.empty_buckets(), m.get_size(), m.get_capacity())

    print("\nPDF - empty_buckets example 2")
    print("-----------------------------")
    m = HashMap(53, hash_function_1)
    for i in range(150):
        m.put('key' + str(i), i * 100)
        if i % 30 == 0:
            print(m.empty_buckets(), m.get_size(), m.get_capacity())

    print("\nPDF - resize example 1")
    print("----------------------")
    m = HashMap(23, hash_function_1)
    m.put('key1', 10)
    print(m.get_size(), m.get_capacity(), m.get('key1'), m.contains_key('key1'))
    m.resize_table(30)
    print(m.get_size(), m.get_capacity(), m.get('key1'), m.contains_key('key1'))

    print("\nPDF - resize example 2")
    print("----------------------")
    m = HashMap(79, hash_function_2)
    keys = [i for i in range(1, 1000, 13)]
    for key in keys:
        m.put(str(key), key * 42)
    print(m.get_size(), m.get_capacity())

    for capacity in range(111, 1000, 117):
        m.resize_table(capacity)

        if m.table_load() > 0.5:
            print(f"Check that the load factor is acceptable after the call to resize_table().\n"
                  f"Your load factor is {round(m.table_load(), 2)} and should be less than or equal to 0.5")

        m.put('some key', 'some value')
        result = m.contains_key('some key')
        m.remove('some key')

        for key in keys:
            # all inserted keys must be present
            result &= m.contains_key(str(key))
            # NOT inserted keys must be absent
            result &= not m.contains_key(str(key + 1))
        print(capacity, result, m.get_size(), m.get_capacity(), round(m.table_load(), 2))

    print("\nPDF - get example 1")
    print("-------------------")
    m = HashMap(31, hash_function_1)
    print(m.get('key'))
    m.put('key1', 10)
    print(m.get('key1'))

    print("\nPDF - get example 2")
    print("-------------------")
    m = HashMap(151, hash_function_2)
    for i in range(200, 300, 7):
        m.put(str(i), i * 10)
    print(m.get_size(), m.get_capacity())
    for i in range(200, 300, 21):
        print(i, m.get(str(i)), m.get(str(i)) == i * 10)
        print(i + 1, m.get(str(i + 1)), m.get(str(i + 1)) == (i + 1) * 10)

    print("\nPDF - contains_key example 1")
    print("----------------------------")
    m = HashMap(11, hash_function_1)
    print(m.contains_key('key1'))
    m.put('key1', 10)
    m.put('key2', 20)
    m.put('key3', 30)
    print(m.contains_key('key1'))
    print(m.contains_key('key4'))
    print(m.contains_key('key2'))
    print(m.contains_key('key3'))
    m.remove('key3')
    print(m.contains_key('key3'))

    print("\nPDF - contains_key example 2")
    print("----------------------------")
    m = HashMap(79, hash_function_2)
    keys = [i for i in range(1, 1000, 20)]
    for key in keys:
        m.put(str(key), key * 42)
    print(m.get_size(), m.get_capacity())
    result = True
    for key in keys:
        # all inserted keys must be present
        result &= m.contains_key(str(key))
        # NOT inserted keys must be absent
        result &= not m.contains_key(str(key + 1))
    print(result)

    print("\nPDF - remove example 1")
    print("----------------------")
    m = HashMap(53, hash_function_1)
    print(m.get('key1'))
    m.put('key1', 10)
    print(m.get('key1'))
    m.remove('key1')
    print(m.get('key1'))
    m.remove('key4')

    print("\nPDF - clear example 1")
    print("---------------------")
    m = HashMap(101, hash_function_1)
    print(m.get_size(), m.get_capacity())
    m.put('key1', 10)
    m.put('key2', 20)
    m.put('key1', 30)
    print(m.get_size(), m.get_capacity())
    m.clear()
    print(m.get_size(), m.get_capacity())

    print("\nPDF - clear example 2")
    print("---------------------")
    m = HashMap(53, hash_function_1)
    print(m.get_size(), m.get_capacity())
    m.put('key1', 10)
    print(m.get_size(), m.get_capacity())
    m.put('key2', 20)
    print(m.get_size(), m.get_capacity())
    m.resize_table(100)
    print(m.get_size(), m.get_capacity())
    m.clear()
    print(m.get_size(), m.get_capacity())

    print("\nPDF - get_keys_and_values example 1")
    print("------------------------")
    m = HashMap(11, hash_function_2)
    for i in range(1, 6):
        m.put(str(i), str(i * 10))
    print(m.get_keys_and_values())

    m.resize_table(2)
    print(m.get_keys_and_values())

    m.put('20', '200')
    m.remove('1')
    m.resize_table(12)
    print(m.get_keys_and_values())

    print("\nPDF - __iter__(), __next__() example 1")
    print("---------------------")
    m = HashMap(10, hash_function_1)
    for i in range(5):
        m.put(str(i), str(i * 10))
    print(m)
    for item in m:
        print('K:', item.key, 'V:', item.value)

    print("\nPDF - __iter__(), __next__() example 2")
    print("---------------------")
    m = HashMap(10, hash_function_2)
    for i in range(5):
        m.put(str(i), str(i * 24))
    m.remove('0')
    m.remove('4')
    print(m)
    for item in m:
        print('K:', item.key, 'V:', item.value)