Reverse Doubly Linked List in Groups of K

Problem Statement

Pattern:

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Solution

public Node revListInGroupOfGivenSize(Node head, int K){
	Node curr = head, prev = null;
	int count = 0;
	
	// let prev be the leading pointer of the new reversed LL
	// and keep inserting `curr` (leading ptr of leftover LL)
	// before `prev`
	
	while(curr != null && count++ < K) {
		Node next = curr.next;
		
		curr.prev = null;
		curr.next = prev;
		if(prev!=null) prev.prev = curr;
		
		prev = curr;
		curr = next;
	}
	
	if(curr != null) {
		head.next = revListInGroupOfGivenSize(curr, K);
		head.next.prev = head;
	}
	
	return prev;
}

Notes

• much like GFG Reverse Doubly Linked List