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updated docs - double_hash_hash_table

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Krishna Vedala 2020-07-25 10:48:37 -04:00
parent 0c0e07953a
commit 61c5998a16
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1 changed files with 111 additions and 74 deletions
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185
hashing/double_hash_hash_table.cpp
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@ -2,18 +2,13 @@
* @file double_hash_hash_table.cpp
* @author [achance6](https://github.com/achance6)
* @author [Krishna Vedala](https://github.com/kvedala)
* @brief
* @brief Storage mechanism using double-hashed keys.
* @note The implementation can be optimized by using OOP style.
*/
#include <iostream>
#include <memory>
#include <string>
#include <vector>
using std::cin;
using std::cout;
using std::endl;
using std::string;
namespace { // keep the code local to this file by assigning them to an unnamed
// namespace
@ -31,25 +26,42 @@ int tomb = -1;
int size;
bool rehashing;
// Node that holds key
/** Node object that holds key */
struct Entry {
explicit Entry(int key = notPresent) : key(key) {}
int key;
explicit Entry(int key = notPresent) : key(key) {} ///< constructor
int key; ///< key value
};
// Hash a key
/**
* @brief Hash a key. Uses the STL library's `std::hash()` function.
*
* @param key value to hash
* @return hash value of the key
*/
size_t hashFxn(int key) {
std::hash<int> hash;
return hash(key);
}
// Used for second hash function
/**
* @brief Used for second hash function
*
* @param key key value to hash
* @return hash value of the key
*/
size_t otherHashFxn(int key) {
std::hash<int> hash;
return 1 + (7 - (hash(key) % 7));
}
// Performs double hashing to resolve collisions
/**
* @brief Performs double hashing to resolve collisions
*
* @param key key value to apply double-hash on
* @param searching `true` to check for conflicts
* @return Index of key when found
* @return new hash if no conflicts present
*/
int doubleHash(int key, bool searching) {
int hash = static_cast<int>(hashFxn(key));
int i = 0;
@ -63,36 +75,42 @@ int doubleHash(int key, bool searching) {
return notPresent;
}
if (searchingProber(entry, key)) {
cout << "Found key!" << endl;
std::cout << "Found key!" << std::endl;
return index;
}
cout << "Found tombstone or equal hash, checking next" << endl;
std::cout << "Found tombstone or equal hash, checking next"
<< std::endl;
i++;
} else {
if (putProber(entry, key)) {
if (!rehashing) {
cout << "Spot found!" << endl;
std::cout << "Spot found!" << std::endl;
}
return index;
}
if (!rehashing) {
cout << "Spot taken, looking at next (next index:"
<< " "
<< static_cast<int>(hash + (i * otherHashFxn(key))) %
totalSize
<< ")" << endl;
std::cout << "Spot taken, looking at next (next index:"
<< " "
<< static_cast<int>(hash + (i * otherHashFxn(key))) %
totalSize
<< ")" << std::endl;
}
i++;
}
if (i == totalSize * 100) {
cout << "DoubleHash probe failed" << endl;
std::cout << "DoubleHash probe failed" << std::endl;
return notPresent;
}
} while (entry.key != notPresent);
return notPresent;
}
// Finds empty spot
/** Finds empty spot in a vector
* @param entry vector to search in
* @param key key to search for
* @returns `true` if key is not present or is a `toumb`
* @returns `false` is already occupied
*/
bool putProber(Entry entry, int key) {
if (entry.key == notPresent || entry.key == tomb) {
return true;
@ -100,7 +118,12 @@ bool putProber(Entry entry, int key) {
return false;
}
// Looks for a matching key
/** Looks for a matching key
* @param entry vector to search in
* @param key key value to search
* @returns `true` if found
* @returns `false` if not found
*/
bool searchingProber(Entry entry, int key) {
if (entry.key == key) {
return true;
@ -108,23 +131,27 @@ bool searchingProber(Entry entry, int key) {
return false;
}
// Displays the table
/** Displays the table
* @returns None
*/
void display() {
for (int i = 0; i < totalSize; i++) {
if (table[i].key == notPresent) {
cout << " Empty ";
std::cout << " Empty ";
} else if (table[i].key == tomb) {
cout << " Tomb ";
std::cout << " Tomb ";
} else {
cout << " ";
cout << table[i].key;
cout << " ";
std::cout << " ";
std::cout << table[i].key;
std::cout << " ";
}
}
cout << endl;
std::cout << std::endl;
}
// Rehashes the table into a bigger table
/** Rehashes the table into a bigger table
* @returns None
*/
void rehash() {
// Necessary so wall of add info isn't printed all at once
rehashing = true;
@ -143,10 +170,12 @@ void rehash() {
// oldTable.reset();
rehashing = false;
cout << "Table was rehashed, new size is: " << totalSize << 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 add to the table
*/
void add(int key) {
// auto* entry = new Entry();
// entry->key = key;
@ -158,86 +187,94 @@ void add(int key) {
}
}
// Removes key. Leaves tombstone upon removal.
/** Removes key. Leaves tombstone upon removal.
* @param key key value to remove
*/
void remove(int key) {
int index = doubleHash(key, true);
if (index == notPresent) {
cout << "key not found" << endl;
std::cout << "key not found" << std::endl;
}
table[index].key = tomb;
cout << "Removal successful, leaving tombstone" << endl;
std::cout << "Removal successful, leaving tombstone" << std::endl;
size--;
}
// Information about the adding process
/** Information about the adding process
* @param key key value to add to table
*/
void addInfo(int key) {
cout << "Initial table: ";
std::cout << "Initial table: ";
display();
cout << endl;
cout << "hash of " << key << " is " << hashFxn(key) << " % " << totalSize
<< " == " << hashFxn(key) % totalSize;
cout << endl;
std::cout << std::endl;
std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
<< totalSize << " == " << hashFxn(key) % totalSize;
std::cout << std::endl;
add(key);
cout << "New table: ";
std::cout << "New table: ";
display();
}
// Information about removal process
/** Information about removal process
* @param key key value to remove from table
*/
void removalInfo(int key) {
cout << "Initial table: ";
std::cout << "Initial table: ";
display();
cout << endl;
cout << "hash of " << key << " is " << hashFxn(key) << " % " << totalSize
<< " == " << hashFxn(key) % totalSize;
cout << endl;
std::cout << std::endl;
std::cout << "hash of " << key << " is " << hashFxn(key) << " % "
<< totalSize << " == " << hashFxn(key) % totalSize;
std::cout << std::endl;
remove(key);
cout << "New table: ";
std::cout << "New table: ";
display();
}
} // namespace
// I/O
/** Main program
* @returns None
*/
int main() {
int cmd = 0, hash = 0, key = 0;
cout << "Enter the initial size of Hash Table. = ";
cin >> totalSize;
std::cout << "Enter the initial size of Hash Table. = ";
std::cin >> totalSize;
table = std::vector<Entry>(totalSize);
bool loop = true;
while (loop) {
system("pause");
cout << endl;
cout << "PLEASE CHOOSE -" << endl;
cout << "1. Add key. (Numeric only)" << endl;
cout << "2. Remove key." << endl;
cout << "3. Find key." << endl;
cout << "4. Generate Hash. (Numeric only)" << endl;
cout << "5. Display Hash table." << endl;
cout << "6. Exit." << endl;
cin >> cmd;
std::cout << std::endl;
std::cout << "PLEASE CHOOSE -" << std::endl;
std::cout << "1. Add key. (Numeric only)" << std::endl;
std::cout << "2. Remove key." << std::endl;
std::cout << "3. Find key." << std::endl;
std::cout << "4. Generate Hash. (Numeric only)" << std::endl;
std::cout << "5. Display Hash table." << std::endl;
std::cout << "6. Exit." << std::endl;
std::cin >> cmd;
switch (cmd) {
case 1:
cout << "Enter key to add = ";
cin >> key;
std::cout << "Enter key to add = ";
std::cin >> key;
addInfo(key);
break;
case 2:
cout << "Enter key to remove = ";
cin >> key;
std::cout << "Enter key to remove = ";
std::cin >> key;
removalInfo(key);
break;
case 3: {
cout << "Enter key to search = ";
cin >> key;
std::cout << "Enter key to search = ";
std::cin >> key;
Entry entry = table[doubleHash(key, true)];
if (entry.key == notPresent) {
cout << "Key not present";
std::cout << "Key not present";
}
break;
}
case 4:
cout << "Enter element to generate hash = ";
cin >> key;
cout << "Hash of " << key << " is = " << hashFxn(key);
std::cout << "Enter element to generate hash = ";
std::cin >> key;
std::cout << "Hash of " << key << " is = " << hashFxn(key);
break;
case 5:
display();
@ -247,7 +284,7 @@ int main() {
break;
// delete[] table;
}
cout << endl;
std::cout << std::endl;
}
return 0;
}