linear_probing Namespace Reference

An implementation of hash table using linear probing algorithm. More...

Classes
struct	Entry

Functions
bool	putProber (const Entry &entry, int key)
bool	searchingProber (const Entry &entry, int key)
void	add (int key)
size_t	hashFxn (int key)
	Hash a key. Uses the STL library's std::hash() function.
int	linearProbe (int key, bool searching)
void	display ()
void	rehash ()
void	remove (int key)
void	addInfo (int key)
void	removalInfo (int key)

Variables
int	notPresent
std::vector< Entry >	table
int	totalSize
int	tomb = -1
int	size
bool	rehashing

Detailed Description

An implementation of hash table using linear probing algorithm.

Function Documentation

add()

void linear_probing::add

(

int

key

)

Adds entry using linear probing. Checks for load factor here

Parameters

key	key value to hash and add

                  {
    int index = linearProbe(key, false);
    table[index].key = key;
    // Load factor greater than 0.5 causes resizing
    if (++size / static_cast<double>(totalSize) >= 0.5) {
        rehash();
    }
}

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addInfo()

void linear_probing::addInfo

(

int

key

)

Information about the adding process

Parameters

key	key value to hash and add

                      {
    std::cout << "Initial table: ";
    display();
    std::cout << std::endl;
    std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
              << totalSize << " == " << hashFxn(key) % totalSize;
    std::cout << std::endl;
    add(key);
    std::cout << "New table: ";
    display();
}

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display()

void linear_probing::display

(

)

Function to displays the table

Returns

none

               {
    for (int i = 0; i < totalSize; i++) {
        if (table[i].key == notPresent) {
            std::cout << " Empty ";
        } else if (table[i].key == tomb) {
            std::cout << " Tomb ";
        } else {
            std::cout << " ";
            std::cout << table[i].key;
            std::cout << " ";
        }
    }
    std::cout << std::endl;
}

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hashFxn()

size_t linear_probing::hashFxn

(

int

key

)

Hash a key. Uses the STL library's std::hash() function.

Parameters

key	value to hash

Returns

hash value of the key

                        {
    std::hash<int> hash;
    return hash(key);
}

linearProbe()

int linear_probing::linearProbe	(	int	key,
		bool	searching )

Performs linear probing to resolve collisions

Parameters

key	key value to hash

Returns

hash value of the key

                                         {
    int hash = static_cast<int>(hashFxn(key));
    int i = 0;
    Entry entry;
    do {
        int index = static_cast<int>((hash + i) % totalSize);
        entry = table[index];
        if (searching) {
            if (entry.key == notPresent) {
                return notPresent;
            }
            if (searchingProber(entry, key)) {
                std::cout << "Found key!" << std::endl;
                return index;
            }
            std::cout << "Found tombstone or equal hash, checking next"
                      << std::endl;
            i++;
        } else {
            if (putProber(entry, key)) {
                if (!rehashing) {
                    std::cout << "Spot found!" << std::endl;
                }
                return index;
            }
            if (!rehashing) {
                std::cout << "Spot taken, looking at next" << std::endl;
            }
            i++;
        }
        if (i == totalSize) {
            std::cout << "Linear probe failed" << std::endl;
            return notPresent;
        }
    } while (entry.key != notPresent);
    return notPresent;
}

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putProber()

bool linear_probing::putProber	(	const Entry &	entry,
		int	key )

Finds empty spot

Parameters

entry	instance to check in
key	key value to hash

Returns

hash value of the key

                                            {
    if (entry.key == notPresent || entry.key == tomb) {
        return true;
    }
    return false;
}

rehash()

void linear_probing::rehash

(

)

Rehashes the table into a bigger table

Returns

None

              {
    // Necessary so wall of add info isn't printed all at once
    rehashing = true;
    int oldSize = totalSize;
    std::vector<Entry> oldTable(table);
    // Really this should use the next prime number greater than totalSize *
    // 2
    totalSize *= 2;
    table = std::vector<Entry>(totalSize);
    for (int i = 0; i < oldSize; i++) {
        if (oldTable[i].key != -1 && oldTable[i].key != notPresent) {
            size--;  // Size stays the same (add increments size)
            add(oldTable[i].key);
        }
    }
    // delete[] oldTable;
    rehashing = false;
    std::cout << "Table was rehashed, new size is: " << totalSize << std::endl;
}

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removalInfo()

void linear_probing::removalInfo

(

int

key

)

Information about removal process

Parameters

key	key value to hash and remove

                          {
    std::cout << "Initial table: ";
    display();
    std::cout << std::endl;
    std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
              << totalSize << " == " << hashFxn(key) % totalSize;
    std::cout << std::endl;
    remove(key);
    std::cout << "New table: ";
    display();
}

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remove()

void linear_probing::remove

(

int

key

)

Removes key. Leaves tombstone upon removal.

Parameters

key	key value to hash and remove

                     {
    int index = linearProbe(key, true);
    if (index == notPresent) {
        std::cout << "key not found" << std::endl;
    }
    std::cout << "Removal Successful, leaving tomb" << std::endl;
    table[index].key = tomb;
    size--;
}

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searchingProber()

bool linear_probing::searchingProber	(	const Entry &	entry,
		int	key )

Looks for a matching key

Parameters

entry	instance to check in
key	key value to hash

Returns

hash value of the key

                                                  {
    if (entry.key == key) {
        return true;
    }
    return false;
}