Reverse Nodes in k-Group

ListNode.java

package com.interviewbytes.linkedlists;


public class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
    }
}

ReverseKGroup.java

package com.interviewbytes.linkedlists;

public class ReverseKGroup {

    public ListNode reverseKGroup(ListNode head, int k) {

        if (head == null) return null;

        int count = k;

        ListNode current = head;
        while (count > 0 && current != null) {
            current = current.next;
            count--;
        }

        if (count > 0) return head;

        ListNode newHead = null;
        current = head;
        count = k;

        while (count > 0 && current != null) {
            ListNode next = current.next;
            current.next = newHead;
            newHead = current;
            current = next;
            count--;
        }

        if (current != null) head.next = reverseKGroup(current, k);

        return newHead;
    }
}