ListNodePatch 1

ListNode.py

@@ -0,0 +1,54 @@
+# Definition for singly-linked list.
+class ListNode(object):
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class Solution(object):
+    def swapPairs(self, head):
+        """
+        :type head: Optional[ListNode]
+        :rtype: Optional[ListNode]
+        """
+        dummy = ListNode(0)
+        dummy.next = head
+        prev = dummy
+
+        while head and head.next:
+            first = head
+            second = head.next
+
+            # Swapping
+            prev.next = second
+            first.next = second.next
+            second.next = first
+
+            # Move pointers forward
+            prev = first
+            head = first.next
+
+        return dummy.next
+
+
+# Helper functions for testing
+def create_linked_list(values):
+    dummy = ListNode(0)
+    curr = dummy
+    for v in values:
+        curr.next = ListNode(v)
+        curr = curr.next
+    return dummy.next
+
+def print_linked_list(node):
+    res = []
+    while node:
+        res.append(node.val)
+        node = node.next
+    print(res)
+
+
+# Example usage
+head = create_linked_list([1, 2, 3, 4])
+obj = Solution()
+result = obj.swapPairs(head)
+print_linked_list(result)  # Output: [2, 1, 4, 3]