Swap Nodes in Pairs LeetCode Solution – Queslers

Problem – Swap Nodes in Pairs LeetCode Solution

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

Swap Nodes in Pairs LeetCode Solution in C++

ListNode* swapPairs(ListNode* head) {
        if(!head || !head->next) return head; //If there are less than 2 nodes in the given nodes, then no need to do anything just return the list as it is.
		
        ListNode* dummyNode = new ListNode();
        
        ListNode* prevNode=dummyNode;
        ListNode* currNode=head;
        
        while(currNode && currNode->next){
            prevNode->next = currNode->next;
            currNode->next = prevNode->next->next;
            prevNode->next->next = currNode;
            
            prevNode = currNode;
            currNode = currNode->next;
        }
        
        return dummyNode->next;
    }

Swap Nodes in Pairs LeetCode Solution in Java

public class Solution {
    public ListNode swapPairs(ListNode head) {
        if ((head == null)||(head.next == null))
            return head;
        ListNode n = head.next;
        head.next = swapPairs(head.next.next);
        n.next = head;
        return n;
    }
}

Swap Nodes in Pairs LeetCode Solution in Python

class Solution(object):
    def swapPairs(self, head):
        if not head or not head.next: return head
        dummy = ListNode(0)
        dummy.next = head
        cur = dummy
        
        while cur.next and cur.next.next:
            first = cur.next
            sec = cur.next.next
            cur.next = sec
            first.next = sec.next
            sec.next = first
            cur = cur.next.next
        return dummy.next       

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