Java中鏈表的實現

Question

我正在閱讀有關Java中鏈表的信息，我已對此代碼進行了編程，運行它時，我得到3作為輸出，它應該按如下所示打印出插入數字的相反順序： 10 7 3 ..我的代碼有什么問題？

public class List {
    private class ListNode {
        private int contents;
        private ListNode next;

        ListNode(int contents) {
            this.contents = contents;
            this.next = null;
        }
    }

    private ListNode head;

    public List() {
        head = null;
    }

    public void insert(int contents) {

        ListNode newNode = new ListNode(contents);
        if (head == null) {
            head = newNode;
        }

        ListNode current = head;
        while (current != null) {
            current = current.next;
        }

        current = newNode;

    }

    public void reverse() {

        ListNode current = head;
        ListNode nodeNext = current.next;

        while (nodeNext != null) {
            current.next = null;
            nodeNext.next = current;
            current = nodeNext;
        }

        head = current;
    }

    public String toString() {

        String s = "";
        ListNode current = head;
        while (current != null) {
            s = current.contents + s;
            current = current.next;
        }

        return s;
    }

    public static void main(String[] args) {

        List l = new List();
        l.insert(3);
        l.insert(7);
        l.insert(10);
        l.reverse();
        System.out.println(l.toString());

    }
}

謝謝

Answer 1

您的insert方法不會將新節點連接到現有列表的最后一個節點。 您必須將新節點分配給現有列表的最后一個節點的node.next ：

public void insert(int contents) {

    ListNode newNode = new ListNode(contents);
    if (head == null) {
        head = newNode;
        return;
    }

    ListNode current = head;
    while (current.next != null) {
        current = current.next;
    }

    current.next = newNode;

}

Answer 2

private ListNode head;
private ListNode tail;
public void insert(int contents) {

    ListNode newNode = new ListNode(contents);
    if (head == null) {
        head = newNode;
        tail = newNode;
        return;
    }
    tail.next = newNode;
    tail = newNode;
}

保留用於O（1）插入的尾節點引用。

您的reverse()方法有點錯誤：

// this loop will run forever if there are more than 1 nodes
while (nodeNext != null) {
    current.next = null;
    nodeNext.next = current; // you lose the reference to the entire list here
    current = nodeNext;
}

重寫函數：

public void reverse() {
    ListNode cursor = head;
    ListNode newHead = null;

    while (cursor != null) {
        ListNode next = cursor.next;
        cursor.next = newHead;
        newHead = cursor;
        cursor = next;
    }
    head = newHead;
}

這樣做cursor.next = newHead ，失去原有的參考cursor.next 。 所以你需要采取的參考cursor.next在臨時變量： ListNode next = cursor.next;

打印功能

public void print() {
    ListNode cursor = head;
    while (cursor != null) {
        System.out.println(cursor.contents);
        cursor = cursor.next;
    }
}