Swap Nodes in Pairs - Recursion

Linked List     Medium     Recursion    

Problem Statement:

Given a linked list, swap every two adjacent nodes and return its head. You must solve the problem without modifying the values in the list's nodes (i.e., only nodes themselves may be changed.)

 

Example 1:

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

Example 2:

Input: head = []
Output: []

Example 3:

Input: head = [1]
Output: [1]

 

Constraints:

• The number of nodes in the list is in the range [0, 100].
• 0 <= Node.val <= 100

Solution:

ListNode* swapPairs(ListNode* head) 
{
	if (head==NULL || head->next==NULL) return head;
	ListNode *res = new ListNode(head->next->val);
	res->next = new ListNode(head->val);
	res->next->next = swapPairs(head->next->next);
	return res;
}