Remove duplicate nodes with the use of a HashMap array

RemoveDuplicatesHashMap.java

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// Node class
static class Node {

	int data;

	Node next;

	public Node(int data){
		this.data = data;
		this.next = null;
	}
}


static Node removeDuplicates(Node head){

	// null check here
	if(head == null || head.next == null) return head;

	// create a temporary node
	Node next = head;

	// create HashMap array
	HashMap<Integer, Integer> map = new HashMap<>();

	// insert node in map
	map.put(next.data, 1);

	// iterate list and insert rest of nodes in map
	while(next.next != null){

		// check if node already exists in map
		if(!map.containsKey(next.next.data)){
			map.put(next.next.data, 1);
			next = next.next;
		} else {
			next.next = next.next.next;
		}
	}

	// return the head of list
	return head;
}

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