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  1. Prepare
  2. Data Structures
  3. Linked Lists
  4. Reverse a doubly linked list
  5. Discussions

Reverse a doubly linked list

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  • carlbidwell268
     + 0 comments

    Reversing a doubly linked list is all about carefully swapping next and prev for each node, one wrong move and the whole chain breaks. How did you handle the pointer swap without losing track of the list?

  • shinderohitd19
     + 0 comments

    Simple java solution TC-O(N) SC-O(1)

    public static DoublyLinkedListNode reverse(DoublyLinkedListNode llist) {
        if(llist == null || llist.next == null){
            return llist;
        }
        DoublyLinkedListNode last = null;
        DoublyLinkedListNode curr = llist;
        
        while(curr!=null){
            last = curr.prev;
            curr.prev = curr.next;
            curr.next = last;
            curr = curr.prev;
        }
        return last.prev;
    }

}

  • mdsanz
     + 0 comments

    My Java 8 Solution

    public static DoublyLinkedListNode reverse(DoublyLinkedListNode llist) {
        DoublyLinkedListNode reversedList = null, current = llist;
        
        while (current != null) {
            DoublyLinkedListNode temp = new DoublyLinkedListNode(current.data);
            
            if (reversedList == null) {
                reversedList = temp;
            } else {
                temp.next = reversedList;
                reversedList.prev = temp;
                reversedList = reversedList.prev;
            }
            current = current.next;
        }
        
        return reversedList;
    }

  • limkevinkuan
     + 0 comments

    PSA: DO NOT USE KOTLIN

    You cannot pass using Kotlin due to this issue, which still remains today.

  • emhhacker
     + 0 comments

    My Java solution with linear time complexity and constant space complexity:

     public static DoublyLinkedListNode reverse(DoublyLinkedListNode llist) {
        //return llist if its null, indicating the llist is empty
        if(llist == null) return llist;
        
        //use a curr ptr
        DoublyLinkedListNode curr = llist;
        
        //iterate thru the llist
        while(curr != null){
            //store curr nxt in a temp var
            DoublyLinkedListNode temp = curr.next;
            curr.next = curr.prev;
            curr.prev = temp;
            
            if(temp == null) break;
            else curr = temp;
        }
        return curr;        
    }