Question

Suppose that you want to write a method that searches for an item in a generic DLL and returns the pointer to the target (if search succeeds) or null (if search fails).

One strategy to improve the performance of the search algorithm is, whenever you have a successful search, you move the target one step towards the front of the list. You can implement helper methods.

Example:
7 <--> 5 <--> 0 <--> 11

Search for 0: SUCCESS!
7 <--> 0 <--> 5 <--> 11

Search for 11: SUCCESS!
7 <--> 0 <--> 11 <--> 5

Search for 6: FAIL!
7 <--> 0 <--> 11 <--> 5

Write the method for this improved search method.

    public class DLLNode<T> {
        public T data;
        public DLLNode<T> prev, next;
    
        public DLLNode(T data, DLLNode<T> prev, DLLNode<T> next) {
            this.data=data; this.prev=prev; this.next=next;
    }

The next of the last node will be null, and the prev of the first node will be null.

      // moves target one step towards the front of DLL after a successful searches
      public static DLLNode<T> improvedSearch(T target) {
            /** COMPLETE THIS METHOD **/
      }

Answer 1

public class DLLNode<T> {
    public T data;
    public DLLNode<T> prev, next;

    public DLLNode(T data, DLLNode<T> prev, DLLNode<T> next) {
        this.data = data;
        this.prev = prev;
        this.next = next;
    }

    // The next of the last node will be null, and the prev of the first node will be null.
    
    // moves target one step towards the front of DLL after a successful searches
    public DLLNode<T> improvedSearch(T target) {
        if(data.equals(target)) {
            return this;
        }
        if(next == null) {
            return null;
        }
        return next.improvedSearch(target);
    }
}

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