Question

我在创建将项目添加到Java中的最后一个元素之前的方法时遇到了麻烦。我已经有了在链表中添加最后一个元素的代码。

我应如何实施addBeforeLast？

public class LinkedList {
    Node first;
    int size = 0;

    public void addLast(int item) {
        // If the list is empty, just create a node and make it
        // the first.
        if(first == null) {
            first = new Node(item, null);
        } else {
           // Otherwise, find the last node
            Node current = first;
            // Stop when current's next is null: that's how
            // we know it's the last element.
            while(current.next != null) {
                current = current.next;
            }
             Node prev = current;
            // At this point, current is the last node.
            // Make it point to a new node that will contain
            // the given item.
            current.next = new Node(item, prev);
        }
        size++;
    }
}

Answer 1

尝试这样：

public void addBeforeLast(int a) {
    if (first == null) throw new IllegalStateException("There is no last node"); // we cannot addBeforeLast when there is no last;
    if (first.next == null) { // when only single node, we have to update first;
        first = new Node(a, first);
        return;
    }
    Node p = first;
    while (p.next.next != null) p = p.next; // p.next will be the last node now;
    p.next = new Node(a, p.next);
}

节点将具有以下构造函数：

    public Node(int theVal, Node theNext) {
        this.val = theVal;
        this.next = theNext;
    }

顺便说一句，即使在addBeforeLast没有节点的情况下，如果您坚持要添加新节点。您可以使用此方法：

public void addBeforeLast(int a) {
    if (first == null || first.next == null) { // we have to update first;
        first = new Node(a, first);
        return;
    }
    Node p = first;
    while (p.next.next != null) p = p.next; // p.next will be the last node now;
    p.next = new Node(a, p.next);
}

如何在链表中的最后一个节点之前插入节点？

1 个答案: