Reverse Linked List

Author: Shikha-code36

Recursion/Linked-List/Reverse-Linked-List.py

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+'''
+Given pointer to the head node of a linked list, the task is to recursively reverse the linked list. We need to reverse the list by changing links between nodes.
+
+Examples:
+
+Input : Head of following linked list  
+       1->2->3->4->NULL
+Output : Linked list should be changed to,
+       4->3->2->1->NULL
+
+'''
+
+
+'''Recursive Approach'''
+
+
+def reverseList(head):
+
+    if not head:
+        return None
+
+    newHead = head  # head is current node that we are at in our recursive call
+    if head.next:  # if we keep reversing
+        newHead = reverseList(head.next)  # now the result will be new head
+        head.next.next = head  # reversing the link between the next node and head
+    head.next = None  # if head happens to be the first node in the list we're setting the next pointer to null
+
+    return newHead  # reverse the list and return the new head
+
+
+'''Iterative Approach'''
+
+
+def reverseList(head):
+    prev, curr = None, head
+
+    while curr:
+        temp = curr.next
+        curr.next = prev
+        prev = curr
+        curr = temp
+    return prev