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HashTable.java
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173 lines (151 loc) · 3.71 KB
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package datastructure.hashtable;
import java.util.ArrayList;
/**
* The type Hash table.
*/
public class HashTable {
/**
* The Bucket.
*/
private static ArrayList<HashEntry> bucket;
/**
* The Slots.
*/
private static int slots;
/**
* The Size.
*/
private static int size;
/**
* Instantiates a new Hash table.
*/
//Constructor
public HashTable() {
bucket = new ArrayList<HashEntry>();
slots = 10;
size = 0;
//initialize buckets
for (int i = 0; i < slots; i++)
bucket.add(null);
}
/**
* Size int.
*
* @return the int
*/
public int size() {
return size;
}
/**
* Is empty boolean.
*
* @return the boolean
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Gets index.
*
* @param key the key
* @return the index
*/
private static int getIndex(String key) {
//hashCode is a built in function of Strings
int hashCode = key.hashCode();
int index = hashCode % slots;
//Check if index is negative
if (index < 0) {
index = (index + slots) % slots;
}
return index;
}
/**
* Insert.
*
* @param key the key
* @param value the value
*/
public static void insert(String key, int value) {
int bIndex = getIndex(key);
HashEntry head = bucket.get(bIndex);
while (head != null) {
if (head.key.equals(key))
head.value = value;
head = head.next;
}
size++;
head = bucket.get(bIndex);
HashEntry newSlot = new HashEntry(key, value);
bucket.set(bIndex, newSlot);
//Checks if array >60% of the array gets filled
if ((1.0 * size) / slots >= 0.6) {
ArrayList<HashEntry> temp = bucket;
bucket = new ArrayList();
slots = 2 * slots;
size = 0;
for (int i = 0; i < slots; i++)
bucket.add(null);
for (HashEntry head_Node : temp) {
while (head_Node != null) {
insert(head_Node.key, head_Node.value);
head_Node = head_Node.next;
}
}
}
}
/**
* Gets value.
*
* @param key the key
* @return the value
*/
// Return a value for a given key
public int getValue(String key) {
// Find the head of chain
int b_Index = getIndex(key);
HashEntry head = bucket.get(b_Index);
// Search key in the slots
while (head != null) {
if (head.key.equals(key))
return head.value;
head = head.next;
}
// If key not found
return -1;
}
/**
* Delete int.
*
* @param key the key
* @return the int
*/
//Remove a value based with key
public int delete(String key) {
//Find index
int b_Index = getIndex(key);
// Get head of the chain for that index
HashEntry head = bucket.get(b_Index);
//Find the key in slots
HashEntry prev = null;
while (head != null) {
//If key exists
if (head.key.equals(key))
break;
// Else keep moving in chain
prev = head;
head = head.next;
}
// If key does not exist
if (head == null)
return 0;
// Decrease the size by one
size--;
// Remove key
if (prev != null)
prev.next = head.next;
else
bucket.set(b_Index, head.next);
return head.value;
}
}