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280 lines
7.8 KiB
C++
280 lines
7.8 KiB
C++
/**
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* @file
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* @author [achance6](https://github.com/achance6)
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* @author [Krishna Vedala](https://github.com/kvedala)
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* @brief Storage mechanism using [linear probing
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* hash](https://en.wikipedia.org/wiki/Linear_probing) keys.
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* @note The implementation can be optimized by using OOP style.
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*/
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#include <iostream>
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#include <vector>
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/**
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* @addtogroup Open Addressing
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* @{
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* @namespace linear_probing
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* @brief An implementation of hash table using [linear
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* probing](https://en.wikipedia.org/wiki/Linear_probing) algorithm.
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*/
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namespace linear_probing {
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// fwd declarations
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using Entry = struct Entry;
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bool putProber(const Entry& entry, int key);
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bool searchingProber(const Entry& entry, int key);
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void add(int key);
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// Undocumented globals
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int notPresent;
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std::vector<Entry> table;
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int totalSize;
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int tomb = -1;
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int size;
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bool rehashing;
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/** Node object that holds key */
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struct Entry {
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explicit Entry(int key = notPresent) : key(key) {} ///< constructor
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int key; ///< key value
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};
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/**
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* @brief Hash a key. Uses the STL library's `std::hash()` function.
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*
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* @param key value to hash
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* @return hash value of the key
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*/
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size_t hashFxn(int key) {
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std::hash<int> hash;
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return hash(key);
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}
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/** Performs linear probing to resolve collisions
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* @param key key value to hash
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* @return hash value of the key
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*/
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int linearProbe(int key, bool searching) {
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int hash = static_cast<int>(hashFxn(key));
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int i = 0;
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Entry entry;
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do {
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int index = static_cast<int>((hash + i) % totalSize);
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entry = table[index];
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if (searching) {
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if (entry.key == notPresent) {
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return notPresent;
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}
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if (searchingProber(entry, key)) {
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std::cout << "Found key!" << std::endl;
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return index;
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}
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std::cout << "Found tombstone or equal hash, checking next"
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<< std::endl;
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i++;
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} else {
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if (putProber(entry, key)) {
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if (!rehashing) {
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std::cout << "Spot found!" << std::endl;
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}
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return index;
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}
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if (!rehashing) {
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std::cout << "Spot taken, looking at next" << std::endl;
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}
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i++;
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}
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if (i == totalSize) {
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std::cout << "Linear probe failed" << std::endl;
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return notPresent;
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}
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} while (entry.key != notPresent);
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return notPresent;
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}
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/** Finds empty spot
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* @param entry instance to check in
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* @param key key value to hash
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* @return hash value of the key
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*/
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bool putProber(const Entry& entry, int key) {
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if (entry.key == notPresent || entry.key == tomb) {
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return true;
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}
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return false;
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}
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/** Looks for a matching key
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* @param entry instance to check in
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* @param key key value to hash
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* @return hash value of the key
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*/
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bool searchingProber(const Entry& entry, int key) {
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if (entry.key == key) {
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return true;
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}
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return false;
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}
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/** Function to displays the table
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* @returns none
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*/
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void display() {
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for (int i = 0; i < totalSize; i++) {
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if (table[i].key == notPresent) {
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std::cout << " Empty ";
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} else if (table[i].key == tomb) {
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std::cout << " Tomb ";
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} else {
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std::cout << " ";
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std::cout << table[i].key;
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std::cout << " ";
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}
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}
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std::cout << std::endl;
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}
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/** Rehashes the table into a bigger table
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* @returns None
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*/
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void rehash() {
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// Necessary so wall of add info isn't printed all at once
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rehashing = true;
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int oldSize = totalSize;
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std::vector<Entry> oldTable(table);
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// Really this should use the next prime number greater than totalSize *
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// 2
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totalSize *= 2;
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table = std::vector<Entry>(totalSize);
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for (int i = 0; i < oldSize; i++) {
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if (oldTable[i].key != -1 && oldTable[i].key != notPresent) {
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size--; // Size stays the same (add increments size)
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add(oldTable[i].key);
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}
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}
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// delete[] oldTable;
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rehashing = false;
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std::cout << "Table was rehashed, new size is: " << totalSize << std::endl;
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}
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/** Adds entry using linear probing. Checks for load factor here
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* @param key key value to hash and add
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*/
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void add(int key) {
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int index = linearProbe(key, false);
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table[index].key = key;
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// Load factor greater than 0.5 causes resizing
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if (++size / static_cast<double>(totalSize) >= 0.5) {
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rehash();
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}
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}
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/** Removes key. Leaves tombstone upon removal.
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* @param key key value to hash and remove
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*/
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void remove(int key) {
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int index = linearProbe(key, true);
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if (index == notPresent) {
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std::cout << "key not found" << std::endl;
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}
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std::cout << "Removal Successful, leaving tomb" << std::endl;
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table[index].key = tomb;
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size--;
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}
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/** Information about the adding process
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* @param key key value to hash and add
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*/
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void addInfo(int key) {
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std::cout << "Initial table: ";
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display();
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std::cout << std::endl;
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std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
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<< totalSize << " == " << hashFxn(key) % totalSize;
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std::cout << std::endl;
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add(key);
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std::cout << "New table: ";
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display();
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}
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/** Information about removal process
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* @param key key value to hash and remove
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*/
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void removalInfo(int key) {
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std::cout << "Initial table: ";
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display();
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std::cout << std::endl;
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std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
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<< totalSize << " == " << hashFxn(key) % totalSize;
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std::cout << std::endl;
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remove(key);
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std::cout << "New table: ";
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display();
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}
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} // namespace linear_probing
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/**
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* @}
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*/
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using linear_probing::Entry;
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using linear_probing::table;
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using linear_probing::totalSize;
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/** Main function
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* @returns 0 on success
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*/
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int main() {
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int cmd = 0, hash = 0, key = 0;
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std::cout << "Enter the initial size of Hash Table. = ";
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std::cin >> totalSize;
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table = std::vector<Entry>(totalSize);
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bool loop = true;
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while (loop) {
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std::cout << "\nPress a key to continue...\n";
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std::cin.get();
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std::cout << std::endl;
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std::cout << "PLEASE CHOOSE -" << std::endl;
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std::cout << "1. Add key. (Numeric only)" << std::endl;
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std::cout << "2. Remove key." << std::endl;
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std::cout << "3. Find key." << std::endl;
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std::cout << "4. Generate Hash. (Numeric only)" << std::endl;
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std::cout << "5. Display Hash table." << std::endl;
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std::cout << "6. Exit." << std::endl;
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std::cin >> cmd;
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switch (cmd) {
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case 1:
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std::cout << "Enter key to add = ";
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std::cin >> key;
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linear_probing::addInfo(key);
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break;
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case 2:
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std::cout << "Enter key to remove = ";
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std::cin >> key;
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linear_probing::removalInfo(key);
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break;
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case 3: {
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std::cout << "Enter key to search = ";
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std::cin >> key;
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Entry entry = table[linear_probing::linearProbe(key, true)];
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if (entry.key == linear_probing::notPresent) {
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std::cout << "Key not present";
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}
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break;
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}
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case 4:
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std::cout << "Enter element to generate hash = ";
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std::cin >> key;
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std::cout << "Hash of " << key
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<< " is = " << linear_probing::hashFxn(key);
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break;
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case 5:
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linear_probing::display();
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break;
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default:
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loop = false;
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break;
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// delete[] table;
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}
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std::cout << std::endl;
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}
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return 0;
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}
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