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fixed code fir linear_probing....

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Krishna Vedala 2020-07-23 18:16:56 -04:00
parent abfe9ad081
commit d955a49de9
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GPG Key ID: BA19ACF8FC8792F7
1 changed files with 62 additions and 53 deletions
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115
hashing/linear_probing_hash_table.cpp
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@ -1,24 +1,30 @@
// Copyright 2019 /**
* @file
#include <stdlib.h> * @author [achance6](https://github.com/achance6)
#include <functional> * @author [Krishna Vedala](https://github.com/kvedala)
* @brief
*/
#include <iostream> #include <iostream>
#include <string> #include <string>
#include <vector>
using std::cin; using std::cin;
using std::cout; using std::cout;
using std::endl; using std::endl;
using std::string; using std::string;
namespace { // keep the code local to this file by assigning them to an unnamed
// namespace
// fwd declarations // fwd declarations
struct Entry; using Entry = struct Entry;
bool putProber(Entry entry, int key); bool putProber(Entry entry, int key);
bool searchingProber(Entry entry, int key); bool searchingProber(Entry entry, int key);
void add(int key); void add(int key);
// globals // globals
int notPresent; int notPresent;
struct Entry* table; std::vector<Entry> table;
int totalSize; int totalSize;
int tomb = -1; int tomb = -1;
int size; int size;
@ -31,18 +37,18 @@ struct Entry {
}; };
// Hash a key // Hash a key
int hashFxn(int key) { size_t hashFxn(int key) {
std::hash<int> hash; std::hash<int> hash;
return hash(key); return hash(key);
} }
// Performs linear probing to resolve collisions // Performs linear probing to resolve collisions
int linearProbe(int key, bool searching) { int linearProbe(int key, bool searching) {
int hash = static_cast<int>(fabs(hashFxn(key))); int hash = static_cast<int>(hashFxn(key));
int i = 0; int i = 0;
Entry entry; Entry entry;
do { do {
int index = static_cast<int>(fabs((hash + i) % totalSize)); int index = static_cast<int>((hash + i) % totalSize);
entry = table[index]; entry = table[index];
if (searching) { if (searching) {
if (entry.key == notPresent) { if (entry.key == notPresent) {
@ -56,12 +62,14 @@ int linearProbe(int key, bool searching) {
i++; i++;
} else { } else {
if (putProber(entry, key)) { if (putProber(entry, key)) {
if (!rehashing) if (!rehashing) {
cout << "Spot found!" << endl; cout << "Spot found!" << endl;
}
return index; return index;
} }
if (!rehashing) if (!rehashing) {
cout << "Spot taken, looking at next" << endl; cout << "Spot taken, looking at next" << endl;
}
i++; i++;
} }
if (i == totalSize) { if (i == totalSize) {
@ -82,8 +90,9 @@ bool putProber(Entry entry, int key) {
// Looks for a matching key // Looks for a matching key
bool searchingProber(Entry entry, int key) { bool searchingProber(Entry entry, int key) {
if (entry.key == key) if (entry.key == key) {
return true; return true;
}
return false; return false;
} }
@ -108,27 +117,26 @@ 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;
int oldSize = totalSize; int oldSize = totalSize;
Entry* oldTable = table; std::vector<Entry> oldTable(table);
// Really this should use the next prime number greater than totalSize * 2 // Really this should use the next prime number greater than totalSize *
table = new Entry[totalSize * 2]; // 2
totalSize *= 2; totalSize *= 2;
table = std::vector<Entry>(totalSize);
for (int i = 0; i < oldSize; i++) { for (int i = 0; i < oldSize; i++) {
if (oldTable[i].key != -1 && oldTable[i].key != notPresent) { if (oldTable[i].key != -1 && oldTable[i].key != notPresent) {
size--; // Size stays the same (add increments size) size--; // Size stays the same (add increments size)
add(oldTable[i].key); add(oldTable[i].key);
} }
} }
delete[] oldTable; // delete[] oldTable;
rehashing = false; rehashing = false;
cout << "Table was rehashed, new size is: " << totalSize << endl; cout << "Table was rehashed, new size is: " << totalSize << endl;
} }
// Adds entry using linear probing. Checks for load factor here // Adds entry using linear probing. Checks for load factor here
void add(int key) { void add(int key) {
Entry* entry = new Entry();
entry->key = key;
int index = linearProbe(key, false); int index = linearProbe(key, false);
table[index] = *entry; table[index].key = key;
// Load factor greater than 0.5 causes resizing // Load factor greater than 0.5 causes resizing
if (++size / static_cast<double>(totalSize) >= 0.5) { if (++size / static_cast<double>(totalSize) >= 0.5) {
rehash(); rehash();
@ -152,7 +160,7 @@ void addInfo(int key) {
display(); display();
cout << endl; cout << endl;
cout << "hash of " << key << " is " << hashFxn(key) << " % " << totalSize cout << "hash of " << key << " is " << hashFxn(key) << " % " << totalSize
<< " == " << fabs(hashFxn(key) % totalSize); << " == " << hashFxn(key) % totalSize;
cout << endl; cout << endl;
add(key); add(key);
cout << "New table: "; cout << "New table: ";
@ -171,13 +179,14 @@ void removalInfo(int key) {
cout << "New table: "; cout << "New table: ";
display(); display();
} }
} // namespace
// I/O // I/O
int main(void) { int main() {
int cmd, hash, key; int cmd = 0, hash = 0, key = 0;
cout << "Enter the initial size of Hash Table. = "; cout << "Enter the initial size of Hash Table. = ";
cin >> totalSize; cin >> totalSize;
table = new Entry[totalSize]; table = std::vector<Entry>(totalSize);
bool loop = true; bool loop = true;
while (loop) { while (loop) {
system("pause"); system("pause");
@ -191,37 +200,37 @@ int main(void) {
cout << "6. Exit." << endl; cout << "6. Exit." << endl;
cin >> cmd; cin >> cmd;
switch (cmd) { switch (cmd) {
case 1: case 1:
cout << "Enter key to add = "; cout << "Enter key to add = ";
cin >> key; cin >> key;
addInfo(key); addInfo(key);
break; break;
case 2: case 2:
cout << "Enter key to remove = "; cout << "Enter key to remove = ";
cin >> key; cin >> key;
removalInfo(key); removalInfo(key);
break; break;
case 3: { case 3: {
cout << "Enter key to search = "; cout << "Enter key to search = ";
cin >> key; cin >> key;
Entry entry = table[linearProbe(key, true)]; Entry entry = table[linearProbe(key, true)];
if (entry.key == notPresent) { if (entry.key == notPresent) {
cout << "Key not present"; cout << "Key not present";
}
break;
} }
break; case 4:
} cout << "Enter element to generate hash = ";
case 4: cin >> key;
cout << "Enter element to generate hash = "; cout << "Hash of " << key << " is = " << hashFxn(key);
cin >> key; break;
cout << "Hash of " << key << " is = " << fabs(hashFxn(key)); case 5:
break; display();
case 5: break;
display(); default:
break; loop = false;
default: break;
loop = false; // delete[] table;
break;
delete[] table;
} }
cout << endl; cout << endl;
} }