From e2a94da27f058e4238e8c72ead848559d85a0426 Mon Sep 17 00:00:00 2001 From: Krishna Vedala <7001608+kvedala@users.noreply.github.com> Date: Thu, 23 Jul 2020 17:58:14 -0400 Subject: [PATCH] fix double_hash_... --- hashing/double_hash_hash_table.cpp | 122 ++++++++++++++++------------- 1 file changed, 68 insertions(+), 54 deletions(-) diff --git a/hashing/double_hash_hash_table.cpp b/hashing/double_hash_hash_table.cpp index 7ee2757de..26a1150a8 100644 --- a/hashing/double_hash_hash_table.cpp +++ b/hashing/double_hash_hash_table.cpp @@ -1,24 +1,31 @@ -// Copyright 2019 - -#include -#include +/** + * @file double_hash_hash_table.cpp + * @author [achance6](https://github.com/achance6) + * @author [Krishna Vedala](https://github.com/kvedala) + * @brief + */ #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 + // fwd declarations -struct Entry; +using Entry = struct Entry; bool putProber(Entry entry, int key); bool searchingProber(Entry entry, int key); void add(int key); // globals int notPresent; -struct Entry* table; +std::vector table; int totalSize; int tomb = -1; int size; @@ -37,19 +44,20 @@ int hashFxn(int key) { } // Used for second hash function -int otherHashFxn(int key) { +size_t otherHashFxn(int key) { std::hash hash; return 1 + (7 - (hash(key) % 7)); } // Performs double hashing to resolve collisions int doubleHash(int key, bool searching) { - int hash = static_cast(fabs(hashFxn(key))); + int hash = static_cast(std::abs(hashFxn(key))); int i = 0; Entry entry; do { - int index = static_cast(fabs((hash + (i * otherHashFxn(key))))) % - totalSize; + int index = + static_cast(std::abs((hash + (i * otherHashFxn(key))))) % + totalSize; entry = table[index]; if (searching) { if (entry.key == notPresent) { @@ -63,17 +71,19 @@ int doubleHash(int key, bool searching) { i++; } else { if (putProber(entry, key)) { - if (!rehashing) + if (!rehashing) { cout << "Spot found!" << endl; + } return index; } - if (!rehashing) + if (!rehashing) { cout << "Spot taken, looking at next (next index:" << " " << static_cast( - fabs((hash + (i * otherHashFxn(key))))) % + std::abs((hash + (i * otherHashFxn(key))))) % totalSize << ")" << endl; + } i++; } if (i == totalSize * 100) { @@ -94,8 +104,9 @@ bool putProber(Entry entry, int key) { // Looks for a matching key bool searchingProber(Entry entry, int key) { - if (entry.key == key) + if (entry.key == key) { return true; + } return false; } @@ -120,9 +131,9 @@ void rehash() { // Necessary so wall of add info isn't printed all at once rehashing = true; int oldSize = totalSize; - Entry* oldTable = table; + std::vector oldTable(table); // Really this should use the next prime number greater than totalSize * 2 - table = new Entry[totalSize * 2]; + table = std::vector(totalSize * 2); totalSize *= 2; for (int i = 0; i < oldSize; i++) { if (oldTable[i].key != -1 && oldTable[i].key != notPresent) { @@ -130,17 +141,19 @@ void rehash() { add(oldTable[i].key); } } - delete[] oldTable; + // delete[] oldTable; + // oldTable.reset(); + rehashing = false; cout << "Table was rehashed, new size is: " << totalSize << endl; } // Checks for load factor here void add(int key) { - Entry* entry = new Entry(); - entry->key = key; + // auto* entry = new Entry(); + // entry->key = key; int index = doubleHash(key, false); - table[index] = *entry; + table[index].key = key; // Load factor greater than 0.5 causes resizing if (++size / static_cast(totalSize) >= 0.5) { rehash(); @@ -164,7 +177,7 @@ void addInfo(int key) { display(); cout << endl; cout << "hash of " << key << " is " << hashFxn(key) << " % " << totalSize - << " == " << fabs(hashFxn(key) % totalSize); + << " == " << std::abs(hashFxn(key) % totalSize); cout << endl; add(key); cout << "New table: "; @@ -183,13 +196,14 @@ void removalInfo(int key) { cout << "New table: "; display(); } +} // namespace // I/O -int main(void) { - int cmd, hash, key; +int main() { + int cmd = 0, hash = 0, key = 0; cout << "Enter the initial size of Hash Table. = "; cin >> totalSize; - table = new Entry[totalSize]; + table = std::vector(totalSize); bool loop = true; while (loop) { system("pause"); @@ -203,37 +217,37 @@ int main(void) { cout << "6. Exit." << endl; cin >> cmd; switch (cmd) { - case 1: - cout << "Enter key to add = "; - cin >> key; - addInfo(key); - break; - case 2: - cout << "Enter key to remove = "; - cin >> key; - removalInfo(key); - break; - case 3: { - cout << "Enter key to search = "; - cin >> key; - Entry entry = table[doubleHash(key, true)]; - if (entry.key == notPresent) { - cout << "Key not present"; + case 1: + cout << "Enter key to add = "; + cin >> key; + addInfo(key); + break; + case 2: + cout << "Enter key to remove = "; + cin >> key; + removalInfo(key); + break; + case 3: { + cout << "Enter key to search = "; + cin >> key; + Entry entry = table[doubleHash(key, true)]; + if (entry.key == notPresent) { + cout << "Key not present"; + } + break; } - break; - } - case 4: - cout << "Enter element to generate hash = "; - cin >> key; - cout << "Hash of " << key << " is = " << fabs(hashFxn(key)); - break; - case 5: - display(); - break; - default: - loop = false; - break; - delete[] table; + case 4: + cout << "Enter element to generate hash = "; + cin >> key; + cout << "Hash of " << key << " is = " << std::abs(hashFxn(key)); + break; + case 5: + display(); + break; + default: + loop = false; + break; + // delete[] table; } cout << endl; }