From df34c3fdd14d6abeb0208202e0ed114cfbf91fae Mon Sep 17 00:00:00 2001
From: ParitoshAggarwal <paritoshmait@gmail.com>
Date: Sun, 6 Aug 2017 19:46:08 +0530
Subject: [PATCH] Add files via upload

HashMap implemented
Code is working and checked twice to avoid any errors
---
 data_structures/HashMap/HashMap.java | 141 +++++++++++++++++++++++++++
 1 file changed, 141 insertions(+)
 create mode 100644 data_structures/HashMap/HashMap.java

diff --git a/data_structures/HashMap/HashMap.java b/data_structures/HashMap/HashMap.java
new file mode 100644
index 000000000..50856d523
--- /dev/null
+++ b/data_structures/HashMap/HashMap.java
@@ -0,0 +1,141 @@
+package hashmap;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+
+public class HashMap<K,V> {
+	public class hmnodes{ //HashMap nodes 
+		K key;
+		V value;
+	}
+	
+	private int size=0; //size of hashmap
+	private LinkedList<hmnodes> buckets[];  //array of addresses of list
+	
+	public HashMap(){
+		buckets=new LinkedList[4]; //initially create bucket of any size 
+		for(int i=0;i<4;i++)
+			buckets[i]=new LinkedList<>(); 
+	}
+	
+	public void put(K key,V value) throws Exception{
+		int bi=bucketIndex(key); //find the index,the new key will be inserted in linklist at that index
+		int fountAt=find(bi,key); //check if key already exists or not 
+		if(fountAt==-1){
+			hmnodes temp=new hmnodes(); //if doesn't exist create new node and insert 
+			temp.key=key;
+			temp.value=value;
+			buckets[bi].addLast(temp);
+			this.size++;
+		}else{
+			buckets[bi].get(fountAt).value=value;//if already exist modify the value
+		}
+		
+		double lambda = (this.size*1.0)/this.buckets.length;
+		if(lambda>2.0){
+			rehash();  //rehashing function which will increase the size of bucket as soon as lambda exceeds 2.0
+		}
+		
+		return;
+	}
+	
+
+	public V get(K key) throws Exception{
+		int bi=bucketIndex(key);
+		int fountAt=find(bi,key);
+		if(fountAt==-1){
+			return null;
+		}else{
+			return buckets[bi].get(fountAt).value;
+		}
+	}
+	
+	public V remove(K key) throws Exception{
+		int bi=bucketIndex(key);
+		int fountAt=find(bi,key);
+		if(fountAt==-1){
+			return null;
+		}else{
+			this.size--;
+			return buckets[bi].remove(fountAt).value;
+		}
+	}
+	
+	public boolean containskey(K key) throws Exception{
+		int bi=bucketIndex(key);
+		int fountAt=find(bi,key);
+		if(fountAt==-1){
+			return false;
+		}else{
+			return true;
+		}
+	}
+	
+	public int size(){
+		return this.size;
+	}
+	
+	
+	public boolean isempty(){
+		return this.size==0;
+	}
+	
+	public ArrayList<K> keyset() throws Exception{
+		ArrayList<K> arr=new ArrayList<>();
+		for(int i=0;i<buckets.length;i++){
+			for(int j=0;j<buckets[i].size();j++){
+				arr.add(buckets[i].get(j).key);
+			}
+		}
+		return arr;
+	}
+	
+	public ArrayList<V> valueset() throws Exception{
+		ArrayList<V> arr=new ArrayList<>();
+		for(int i=0;i<buckets.length;i++){
+			for(int j=0;j<buckets[i].size();j++){
+				arr.add(buckets[i].get(j).value);
+			}
+		}
+		return arr;
+	}
+	
+	public void display() throws Exception{
+		for(int i=0;i<buckets.length;i++){
+			System.out.print("Bucket: "+i+" ");
+			for(int j=0;j<buckets[i].size();j++){
+				hmnodes temp=buckets[i].get(j);
+				System.out.print("["+temp.key+"->"+temp.value+"]");
+			}
+			System.out.println();
+		}
+	}
+	
+	public int find(int bi,K key) throws Exception{
+		for(int i=0;i<buckets[bi].size();i++){
+			if(key.equals(buckets[bi].get(i).key))
+				return i;
+		}
+		return -1;
+	}
+	
+	public int bucketIndex(K key) throws Exception{
+		int bi=key.hashCode();
+		return Math.abs(bi%buckets.length);
+	}
+
+	private void rehash() throws Exception{
+		LinkedList<hmnodes> ob[]= buckets;
+		buckets=new LinkedList[ob.length*2];
+		for(int i=0;i<ob.length*2;i++)
+			buckets[i]=new LinkedList<>();
+		
+		size = 0;
+		for(int i=0;i<ob.length;i++){
+			for(int j=0;j<ob[i].size();j++){
+				put(ob[i].get(j).key,ob[i].get(j).value);
+			}
+		}
+		
+	}
+}