Find the minimum element in a doubly linked list not working

问题

I have written up this code, to find the minimum of a set of numbers within a linked list.

public DLNode<T> getMinimum() {
    if (isEmpty()) {
        return null;
    }
    DLNode<T> curr = head;
    DLNode<T> min = curr;
    T temporaryMinimum = head.getElement();
    while (curr.getElement() != null) {
        if ((Integer) temporaryMinimum < (Integer) curr.getElement()) {
            min = curr;
        }
        curr = curr.getNext();
    }
    return min;
}

I am testing it using this code block

public static void getMinElement(){
    int[] data = {2, 3, 5, 1, 6};
    //Add elements to the list from array data
    DoublyLinkedList<Integer> ll = new DoublyLinkedList<>();

    for (int i = 0; i < data.length; i++) {
        ll.AddLast(data[i]);
    }

    System.out.println("Size: " + ll.size);

    System.out.println("Minimum Element is: " + ll.getMinimum());

}

called within main like so:

getMinElement();

It does not throw up any errors, but it seems to go into an infinite loop or something (judging by how much CPU is used on my machine whenever I launch it).

I would like to point out that my IDE (IntelliJ IDEA) does not show any errors or warnings of uncontrolled loops or stuff like that. I've been reasoning about it for the past few days, without any luck, and I'm now out of ideas.

Any help is much appreciated.

EDIT: My DLNode Class is:

class DLNode<T> {
    DLNode<T> Element;
    T data;
    DLNode<T> next;
    DLNode<T> prev;

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

    T getElement() {
        return data;
    }
    public DLNode<T> getPrev() {
        return prev;
    }
    public void setPrev(DLNode<T> prev) {
        this.prev = prev;
    }
    public DLNode<T> getNext() {
        return next;
    }
    public void setNext(DLNode<T> next) {
        this.next = next;
    }
}

回答1:

Your loop should be checking if curr != null. Otherwise you will probably get NullPointerException eventually.
Your comparison should be reversed (curr.getElement() should be smaller than temporaryMinimum in order to replace it).
You should modify temporaryMinimum when you find a new minimum.
If your DLNode class is supposed to be generic, you can't cast T to Integer. You can require that T extends Comparable<T>, which would allow you to use compareTo instead of > or <.

Oh, and if you are still getting an infinite loop, perhaps your linked list is circular (i.e. getNext() of the last node returns the first node). I can't be sure without seeing your DoublyLinkedList class.

while (curr != null) {
    if (curr.getElement() != null) {
        if (temporaryMinimum.compareTo(curr.getElement()) > 0) {
            min = curr;
            temporaryMinimum = curr.getElement();
        } 
    }
    curr = curr.getNext();
}

来源：https://stackoverflow.com/questions/47248610/find-the-minimum-element-in-a-doubly-linked-list-not-working

标签

java

doubly-linked-list