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Krishna Vedala 2020-07-29 19:22:05 -04:00
parent d89b2df2f0
commit e09637fb30
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1 changed files with 77 additions and 24 deletions
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101
hashing/quadratic_probing_hash_table.cpp
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@ -10,8 +10,14 @@
#include <iostream> #include <iostream>
#include <vector> #include <vector>
namespace { // keep the code local to this file by assigning them to an unnamed /**
* @addtogroup Open Addressing
* @{
* @namespace quadratic_probing
* @brief An implementation of hash table using [quadratic
* probing](https://en.wikipedia.org/wiki/Quadratic_probing) algorithm.
*/
namespace quadratic_probing {
// fwd declarations // fwd declarations
using Entry = struct Entry; using Entry = struct Entry;
bool putProber(const Entry& entry, int key); bool putProber(const Entry& entry, int key);
@ -26,19 +32,27 @@ int tomb = -1;
int size; int size;
bool rehashing; bool rehashing;
// Node that holds key /** Node that holds key
*/
struct Entry { struct Entry {
explicit Entry(int key = notPresent) : key(key) {} explicit Entry(int key = notPresent) : key(key) {} ///< constructor
int key; int key; ///< key value
}; };
// Hash a key /** Hash a key
* @param key key value to hash
* @returns hash of the key
*/
size_t hashFxn(int key) { size_t hashFxn(int key) {
std::hash<int> hash; std::hash<int> hash;
return hash(key); return hash(key);
} }
// Performs quadratic probing to resolve collisions /** Performs quadratic probing to resolve collisions
* @param key key value to search/probe
* @param searching `true` if only searching, `false1 if assigning
* @returns value of `notPresent`.
*/
int quadraticProbe(int key, bool searching) { int quadraticProbe(int key, bool searching) {
int hash = static_cast<int>(hashFxn(key)); int hash = static_cast<int>(hashFxn(key));
int i = 0; int i = 0;
@ -83,7 +97,12 @@ int quadraticProbe(int key, bool searching) {
return notPresent; return notPresent;
} }
// Finds empty spot /** Finds empty spot
* @param entry Instance of table entry
* @param key key value to search/probe
* @returns `true` if key is present
* @returns `false` if key is absent
*/
bool putProber(const Entry& entry, int key) { bool putProber(const Entry& entry, int key) {
if (entry.key == notPresent || entry.key == tomb) { if (entry.key == notPresent || entry.key == tomb) {
return true; return true;
@ -91,7 +110,12 @@ bool putProber(const Entry& entry, int key) {
return false; return false;
} }
// Looks for a matching key /** Looks for a matching key
* @param entry Instance of table entry
* @param key key value to search/probe
* @returns `true` if key matches the entry
* @returns `false` if key does not match the entry
*/
bool searchingProber(const Entry& entry, int key) { bool searchingProber(const Entry& entry, int key) {
if (entry.key == key) { if (entry.key == key) {
return true; return true;
@ -99,7 +123,11 @@ bool searchingProber(const Entry& entry, int key) {
return false; return false;
} }
// Helper /** Get the entry instance corresponding to a key
* @param key key value to search/probe
* @returns if present, the entry instance
* @returns if not present, a new instance
*/
Entry find(int key) { Entry find(int key) {
int index = quadraticProbe(key, true); int index = quadraticProbe(key, true);
if (index == notPresent) { if (index == notPresent) {
@ -108,7 +136,9 @@ Entry find(int key) {
return table[index]; return table[index];
} }
// Displays the table /** Displays the table
* @returns None
*/
void display() { void display() {
for (int i = 0; i < totalSize; i++) { for (int i = 0; i < totalSize; i++) {
if (table[i].key == notPresent) { if (table[i].key == notPresent) {
@ -124,7 +154,9 @@ void display() {
std::cout << std::endl; std::cout << std::endl;
} }
// Rehashes the table into a bigger table /** Rehashes the table into a bigger table
* @returns none
*/
void rehash() { void rehash() {
// Necessary so wall of add info isn't printed all at once // Necessary so wall of add info isn't printed all at once
rehashing = true; rehashing = true;
@ -144,7 +176,9 @@ void rehash() {
std::cout << "Table was rehashed, new size is: " << totalSize << std::endl; std::cout << "Table was rehashed, new size is: " << totalSize << std::endl;
} }
// Checks for load factor here /** Checks for load factor here
* @param key key value to hash and add to table
*/
void add(int key) { void add(int key) {
int index = quadraticProbe(key, false); int index = quadraticProbe(key, false);
table[index].key = key; table[index].key = key;
@ -154,7 +188,9 @@ void add(int key) {
} }
} }
// Removes key. Leaves tombstone upon removal. /** Removes key. Leaves tombstone upon removal.
* @param key key value to hash and remove from table
*/
void remove(int key) { void remove(int key) {
int index = quadraticProbe(key, true); int index = quadraticProbe(key, true);
if (index == notPresent) { if (index == notPresent) {
@ -165,7 +201,9 @@ void remove(int key) {
size--; size--;
} }
// Information about the adding process /** Information about the adding process
* @param key key value to hash and add to table
*/
void addInfo(int key) { void addInfo(int key) {
std::cout << "Initial table: "; std::cout << "Initial table: ";
display(); display();
@ -178,7 +216,9 @@ void addInfo(int key) {
display(); display();
} }
// Information about removal process /** Information about removal process
* @param key key value to hash and remove from table
*/
void removalInfo(int key) { void removalInfo(int key) {
std::cout << "Initial table: "; std::cout << "Initial table: ";
display(); display();
@ -190,9 +230,19 @@ void removalInfo(int key) {
std::cout << "New table: "; std::cout << "New table: ";
display(); display();
} }
} // namespace
// I/O } // namespace quadratic_probing
/**
* @}
*/
using quadratic_probing::Entry;
using quadratic_probing::table;
using quadratic_probing::totalSize;
/** Main function
* @returns None
*/
int main() { int main() {
int cmd = 0, hash = 0, key = 0; int cmd = 0, hash = 0, key = 0;
std::cout << "Enter the initial size of Hash Table. = "; std::cout << "Enter the initial size of Hash Table. = ";
@ -214,18 +264,20 @@ int main() {
case 1: case 1:
std::cout << "Enter key to add = "; std::cout << "Enter key to add = ";
std::cin >> key; std::cin >> key;
addInfo(key); quadratic_probing::addInfo(key);
break; break;
case 2: case 2:
std::cout << "Enter key to remove = "; std::cout << "Enter key to remove = ";
std::cin >> key; std::cin >> key;
removalInfo(key); quadratic_probing::removalInfo(key);
break; break;
case 3: { case 3: {
std::cout << "Enter key to search = "; std::cout << "Enter key to search = ";
std::cin >> key; std::cin >> key;
Entry entry = table[quadraticProbe(key, true)]; quadratic_probing::Entry entry =
if (entry.key == notPresent) { quadratic_probing::table[quadratic_probing::quadraticProbe(
key, true)];
if (entry.key == quadratic_probing::notPresent) {
std::cout << "Key not present"; std::cout << "Key not present";
} }
break; break;
@ -233,10 +285,11 @@ int main() {
case 4: case 4:
std::cout << "Enter element to generate hash = "; std::cout << "Enter element to generate hash = ";
std::cin >> key; std::cin >> key;
std::cout << "Hash of " << key << " is = " << hashFxn(key); std::cout << "Hash of " << key
<< " is = " << quadratic_probing::hashFxn(key);
break; break;
case 5: case 5:
display(); quadratic_probing::display();
break; break;
default: default:
loop = false; loop = false;