Reverse Nodes in k-Group LeetCode Programming Solutions | LeetCode Problem Solutions in C++, Java, & Python [💯Correct]

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Link for the Problem – Reverse Nodes in k-Group– LeetCode Problem

Reverse Nodes in k-Group– LeetCode Problem

Problem:

Given the head of a linked list, reverse the nodes of the list k at a time, and return the modified list.

k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes, in the end, should remain as it is.

You may not alter the values in the list’s nodes, only nodes themselves may be changed.

Example 1:

Input: head = [1,2,3,4,5], k = 2
Output: [2,1,4,3,5]

Example 2:

Input: head = [1,2,3,4,5], k = 3
Output: [3,2,1,4,5]

Constraints:

• The number of nodes in the list is n.
• 1 <= k <= n <= 5000
• 0 <= Node.val <= 1000

Reverse Nodes in k-Group– LeetCode Solutions

class Solution {
 public:
  ListNode* reverseKGroup(ListNode* head, int k) {
    if (!head || k == 1)
      return head;

    const int length = getLength(head);
    ListNode dummy(0, head);
    ListNode* prev = &dummy;
    ListNode* curr = head;

    for (int i = 0; i < length / k; ++i) {
      for (int j = 0; j < k - 1; ++j) {
        ListNode* next = curr->next;
        curr->next = next->next;
        next->next = prev->next;
        prev->next = next;
      }
      prev = curr;
      curr = curr->next;
    }

    return dummy.next;
  }

 private:
  int getLength(ListNode* head) {
    int length = 0;
    for (ListNode* curr = head; curr; curr = curr->next)
      ++length;
    return length;
  }
};

class Solution {
  public ListNode reverseKGroup(ListNode head, int k) {
    if (head == null || k == 1)
      return head;

    final int length = getLength(head);
    ListNode dummy = new ListNode(0, head);
    ListNode prev = dummy;
    ListNode curr = head;

    for (int i = 0; i < length / k; ++i) {
      for (int j = 0; j < k - 1; ++j) {
        ListNode next = curr.next;
        curr.next = next.next;
        next.next = prev.next;
        prev.next = next;
      }
      prev = curr;
      curr = curr.next;
    }

    return dummy.next;
  }

  private int getLength(ListNode head) {
    int length = 0;
    for (ListNode curr = head; curr != null; curr = curr.next)
      ++length;
    return length;
  }
}

class Solution:
  def reverseKGroup(self, head: ListNode, k: int) -> ListNode:
    if not head or k == 1:
      return head

    def getLength(head: ListNode) -> int:
      length = 0
      while head:
        length += 1
        head = head.next
      return length

    length = getLength(head)
    dummy = ListNode(0, head)
    prev = dummy
    curr = head

    for _ in range(length // k):
      for _ in range(k - 1):
        next = curr.next
        curr.next = next.next
        next.next = prev.next
        prev.next = next
      prev = curr
      curr = curr.next

    return dummy.next