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Author: lmizner

InPlace_Manipulation_LinkedList/swap_pairs.py

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+class LinkedListNode:
+    # __init__ will be used to make a LinkedListNode type object.
+    def __init__(self, data, next=None):
+        self.data = data
+        self.next = next
+
+
+class LinkedList:
+    # __init__ will be used to make a LinkedList type object.
+    def __init__(self):
+        self.head = None
+
+    # insert_node_at_head method will insert a LinkedListNode at head
+    # of a linked list.
+    def insert_node_at_head(self, node):
+        if self.head:
+            node.next = self.head
+            self.head = node
+        else:
+            self.head = node
+
+    # create_linked_list method will create the linked list using the
+    # given integer array with the help of InsertAthead method.
+    def create_linked_list(self, lst):
+        for x in reversed(lst):
+            new_node = LinkedListNode(x)
+            self.insert_node_at_head(new_node)
+    
+    # __str__(self) method will display the elements of linked list.
+    def __str__(self):
+        result = ""
+        temp = self.head
+        while temp:
+            result += str(temp.data)
+            temp = temp.next
+            if temp:
+                result += ", "
+        result += ""
+        return result
+    
+
+def print_list_with_forward_arrow(linked_list_node):
+    temp = linked_list_node
+    while temp:
+        print(temp.data, end=" ")  # print node value
+
+        temp = temp.next
+        if temp:
+            print("→", end=" ")
+        else:
+            # if this is the last node, print null at the end
+            print("→ null", end=" ")
+
+
+def reverse_linked_list(head):
+	prev, curr = None, head
+	while curr:
+		nxt = curr.next
+		curr.next = prev
+		prev = curr
+		curr = nxt
+	return prev
+
+
+def traverse_linked_list(head):
+    current, nxt = head, None
+    while current:
+      nxt = current.next
+      current = nxt
+
+
+
+############################################################ 
+
+
+
+def swap_pairs(head):
+
+    # Verify at least 2 nodes exist
+    if not head or not head.next:
+        return head
+
+    # Initialize dummy node and pointers
+    prev = LinkedListNode(0)  # Dummy node to handle the head
+    prev.next = head
+    current = head
+    new_head = current.next
+
+    # Traverse LinkedList
+    while current and current.next:
+        
+        # Obtain the two nodes that need to be swapped
+        first = current
+        second = current.next
+
+        # Swap the nodes
+        first.next = second.next
+        second.next = first
+
+        # Link previous node to second node
+        prev.next = second
+
+        # Iterate ahead to the next pair of nodes
+        prev = first
+        current = first.next
+
+    # Replace this placeholder return statement with your code
+    return new_head
+
+
+
+# Time Complexity = O(n)
+# Space Complexity = O(1)
+
+
+
+############################################################
+
+
+
+# Driver Cod
+def main():
+    test_cases = [
+        [10, 1, 2, 3, 4, 5],
+        [28, 21, 14, 7],
+        [11, 12, 13, 14, 15],
+        [1, 2]
+    ]
+
+    for idx, test_case in enumerate(test_cases):
+        print(f"Test case {idx + 1}: {test_case}")
+        
+        # Creating a linked list
+        linked_list = LinkedList()
+        linked_list.create_linked_list(test_case)
+
+        # Printing the original linked list
+        print("Original list: ", end="")
+        print_list_with_forward_arrow(linked_list.head)
+        print()  # To add a newline for clarity
+
+        # Swapping pairs
+        swapped_head = swap_pairs(linked_list.head)
+
+        # Printing the swapped linked list
+        print("Swapped list: ", end="")
+        print_list_with_forward_arrow(swapped_head)
+        print("\n")  # To separate test cases
+
+
+if __name__ == '__main__':
+    main()