From 61c5998a1646b7442ed0af73c52d178371d4417e Mon Sep 17 00:00:00 2001 From: Krishna Vedala <7001608+kvedala@users.noreply.github.com> Date: Sat, 25 Jul 2020 10:48:37 -0400 Subject: [PATCH] updated docs - double_hash_hash_table --- hashing/double_hash_hash_table.cpp | 185 +++++++++++++++++------------ 1 file changed, 111 insertions(+), 74 deletions(-) diff --git a/hashing/double_hash_hash_table.cpp b/hashing/double_hash_hash_table.cpp index 5a9615b35..f8c9872d6 100644 --- a/hashing/double_hash_hash_table.cpp +++ b/hashing/double_hash_hash_table.cpp @@ -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 #include -#include #include -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 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 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(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(hash + (i * otherHashFxn(key))) % - totalSize - << ")" << endl; + std::cout << "Spot taken, looking at next (next index:" + << " " + << static_cast(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(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; }