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Data-Structures-Algorithms-Java/Hashmap/HashMap.java at master · indraantoor/Data-Structures-Algorithms-Java · GitHub

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public class HashMap {

// NODE

public class Node {

public String key;

public String value;

private Node next;

public Node(String key, String value) {

this.key = key;

this.value = value;

this.next = null;

}

public void setNextNode(Node node) {

this.next = node;

}

public Node getNextNode() {

return this.next;

}

public void setKeyValue(String key, String value) {

this.key = key;

this.value = value;

}

}

// LINKED LIST

public class LinkedList {

public Node head;

public LinkedList() {

this.head = null;

}

public void addToHead(String key, String value) {

Node newHead = new Node(key, value);

Node currentHead = this.head;

this.head = newHead;

if (currentHead != null) {

this.head.setNextNode(currentHead);

}

}

public void addToTail(String key, String value) {

Node tail = this.head;

if (tail == null) {

this.head = new Node(key, value);

} else {

while (tail.getNextNode() != null) {

tail = tail.getNextNode();

}

tail.setNextNode(new Node(key, value));

}

}

public void removeHead() {

Node removedHead = this.head;

if (removedHead == null) {

return;

}

this.head = removedHead.getNextNode();

}

}

// HASHMAP IMPLEMENTATION

public LinkedList[] hashmap;

public HashMap(int size) {

this.hashmap = new LinkedList[size];

for (int i = 0; i < size; i++) {

this.hashmap[i] = new LinkedList();

}

}

public int hash(String key) {

int hashCode = 0;

for (int i = 0; i < key.length(); i++) {

hashCode = hashCode + Character.codePointAt(key, i);

}

hashCode = hashCode % this.hashmap.length;

return hashCode;

}

public void assign(String key, String value) {

int arrayIndex = this.hash(key);

LinkedList list = this.hashmap[arrayIndex];

if (list.head == null) {

list.addToHead(key, value);

return;

}

Node current = list.head;

while (current != null) {

if (current.key == key) {

current.setKeyValue(key, value);

}

if (current.getNextNode() == null) {

current.setNextNode(new Node(key, value));

break;

}

current = current.getNextNode();

}

}

public String retrieve(String key) {

int arrayIndex = this.hash(key);

Node current = this.hashmap[arrayIndex].head;

while (current != null) {

if (current.key == key) {

return current.value;

}

current = current.getNextNode();

}

return null;

}

public static void main(String[] args) {

HashMap food = new HashMap(2);

food.assign("item1", "pizza");

food.assign("item2", "burger");

System.out.println(food.retrieve("item1"));

System.out.println(food.retrieve("item2"));

}

}

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