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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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698 Discussions

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  • 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;        
    }

  • hayato
     + 0 comments

    my code in go

    func reverse(llist *DoublyLinkedListNode) *DoublyLinkedListNode {
    var last *DoublyLinkedListNode
    for llist != nil {        
        next := llist.next
        
        dumb := llist.prev
        llist.prev = llist.next
        llist.next = dumb
        last = llist
        llist = next
    }
    
    return last
}