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Author: pkprajapati7402

01. Data Structures/06. HashMap/MyHashMap.java

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+package map;
+
+import java.util.ArrayList;
+
+public class MyHashMap<K, V> {
+
+	ArrayList<MapNode<K, V>> buckets;
+	int size; // number of entries
+	int numBuckets; // number of buckets
+
+	public MyHashMap() {
+		numBuckets = 5;
+		buckets = new ArrayList<>();
+		for (int i = 0; i < numBuckets; i++) {
+			buckets.add(null);
+		}
+	}
+
+	private int getBucketIndex(K key) {
+		int hashCode = key.hashCode();
+		return hashCode % numBuckets;
+	}
+
+	public int size() {
+		return size;
+	}
+
+	public double loadFactor() {
+		return (double) size / numBuckets;
+	}
+
+	private void rehash() {
+		System.out.println("\nNumber of Entries = " + size + "\nNumber of Buckets = " + numBuckets + "\nLoad Factor = "
+				+ (double) size / numBuckets);
+		ArrayList<MapNode<K, V>> temp = buckets;
+		buckets = new ArrayList<>();
+		for (int i = 0; i < 2 * numBuckets; i++) {
+			buckets.add(null);
+		}
+		size = 0;
+		numBuckets *= 2;
+		for (int i = 0; i < temp.size(); i++) {
+			MapNode<K, V> curr = temp.get(i);
+			while (curr != null) {
+				K key = curr.key;
+				V value = curr.value;
+				insert(key, value);
+				curr = curr.next;
+			}
+		}
+	}
+
+	public void insert(K key, V value) {
+		int bucketIndex = getBucketIndex(key);
+		MapNode<K, V> curr = buckets.get(bucketIndex); // curr is a pointer which will be used to traverse the
+														// LinkedList
+
+		// traverse through the LinkedList, if the key is found then update it's value
+		while (curr != null) {
+			if (curr.key.equals(key)) {
+				curr.value = value;
+				return;
+			}
+			curr = curr.next;
+		}
+		// if the control comes here, this means that the key is not present in the Map,
+		// so we will create a new MapNode
+		curr = buckets.get(bucketIndex);
+		MapNode<K, V> newElementNode = new MapNode<K, V>(key, value);
+		newElementNode.next = curr;
+		buckets.set(bucketIndex, newElementNode);
+		size++;
+
+		double loadFactor = (double) size / numBuckets;
+		if (loadFactor > 0.7)
+			rehash();
+	}
+
+	public boolean containsKey(K key) {
+		int index = getBucketIndex(key);
+		MapNode<K, V> curr = buckets.get(index); // this is a pointer which will traverse
+		while (curr != null) {
+			// here equals method can be override if you want to use your using your own
+			// class object else Wrapper class like INTEGER, DOUBLE..have their own equals()
+			if (curr.key.equals(key)) {
+				return true;
+			}
+			curr = curr.next;
+		}
+		return false;
+	}
+
+	public V getValue(K key) {
+		int bucketIndex = getBucketIndex(key);
+		MapNode<K, V> curr = buckets.get(bucketIndex); // curr is a pointer which will be used to traverse the
+														// LinkedList
+
+		// traverse through the LinkedList, if the key is found then return its value
+		while (curr != null) {
+			if (curr.key.equals(key)) {
+				return curr.value;
+			}
+			curr = curr.next;
+		}
+		return null;
+	}
+
+	public V remove(K key) {
+		int bucketIndex = getBucketIndex(key);
+		// curr is a pointer which will be used to traverse the LinkedList
+		MapNode<K, V> curr = buckets.get(bucketIndex);
+		// prev is another pointer which will be used to store the location of the
+		// previous node
+		MapNode<K, V> prev = null;
+
+		// traverse through the LinkedList, if the key is found then return its value
+		while (curr != null) {
+			if (curr.key.equals(key)) {
+				if (prev == null)
+					buckets.set(bucketIndex, curr.next);
+				else
+					prev.next = curr.next;
+
+				size--;
+				return curr.value;
+			}
+			prev = curr;
+			curr = curr.next;
+		}
+		return null;
+	}
+
+	public static void main(String[] args) {
+		MyHashMap<String, Integer> map = new MyHashMap<>();
+		for (int i = 1; i <= 20; i++) {
+			map.insert("abc" + i, i);
+			System.out.println("For Entry " + i + " LoadFactor = " + map.loadFactor());
+		}
+		System.out.println(map.containsKey("abc5"));
+		map.remove("abc8");
+		map.remove("abc9");
+		map.remove("abc8");
+
+		for (int i = 0; i < map.size(); i++) {
+			System.out.println("abc" + i + ":" + map.getValue("abc" + i));
+		}
+	}
+
+}
+
+class MapNode<K, V> {
+
+	K key;
+	V value;
+	MapNode<K, V> next;
+
+	public MapNode(K key, V value) {
+		this.key = key;
+		this.value = value;
+	}
+}

01. Data Structures/06. HashMap/README.md

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+## Prerequisite: Learn about Sets in Java
+
+## **STEP 1 : [Complete this awesome playlist by CodingNinja.](https://youtube.com/playlist?list=PLGeDISzAH2BQ59_Cft8hC-HAGbwv8dgQu)**
+
+## **STEP 2 : [Visualize my code here ](./MyHashMap.java)**