迭代链表

Question

我在迭代任务的链表时遇到了一些麻烦。

链表类/节点类（无大小方法，不能修改/添加方法）

class MyGenericLinkedList<S> {
    Node<S> front;
 
    public MyGenericLinkedList() {
        front = null;
    }
 
    public void add(S value) {
        if (front == null) {
            front = new Node<S>(value);
        } else {
            Node<S> current = front;
            while (current.next != null) {
                current = current.next;
            }
            current.next = new Node<S>(value);
        }
    }
 
    public S get(int index) {
        Node<S> current = front;
        for (int i = 0; i < index; i++) {
            current = current.next;
        }
        return (S)current.data;
    }
 
    public void remove(int index) {
        if (index == 0) {
            front = front.next;
        } else {
            Node<S> current = front;
            for (int i = 0; i < index - 1; i++) {
                current = current.next;
            }
            current.next = current.next.next;
        }
    }
}
 
/***  DO NOT MAKE ANY CHANGE TO CLASS Node  ***/
class Node<X> {
    X data;
    Node<X> next;
 
    public Node(X data) {
        this.data = data;
        this.next = null;
    }
 
    public Node(X data, Node<X> next) {
        this.data = data;
        this.next = next;
    }
}

这是我试图用来迭代列表但没有运行的内容

while(node.children.front != null) {
            System.out.println(node.children.front);
            node.children.remove(0);
        }

我的完整java文件：

/***  DO NOT ADD A NEW IMPORT DECLARATION HERE  ***/
 
/***  DO NOT MAKE ANY CHANGE TO CLASS A5 EXCEPT THE PLACEHOLDER TO FILL IN  ***/
/***  YOU CANNOT ADD A NEW FIELD VARIABLE  ***/ 
/***  YOU CANNOT ADD A NEW METHOD DECLARATION  ***/ 
public class A5 {
    public static void main(String[] args) {
        //---------------------------------------------------------------------
        TreeNode root = new TreeNode(1);
        MyGenericLinkedList<TreeNode> children = new MyGenericLinkedList();
 
        TreeNode two = new TreeNode(2);
        TreeNode three = new TreeNode(3);
        TreeNode four = new TreeNode(4);
        TreeNode five = new TreeNode(5);
        TreeNode six = new TreeNode(6);
        TreeNode seven = new TreeNode(7);
        TreeNode eight = new TreeNode(8);
        TreeNode nine = new TreeNode(9);
        TreeNode ten = new TreeNode(10);
        TreeNode eleven = new TreeNode(11);
        TreeNode twelve = new TreeNode(12);
        TreeNode thirteen = new TreeNode(13);
        TreeNode fourteen = new TreeNode(14);
 
        children.add(two);
        children.add(three);
        children.add(four);
        root.setChildren(children);
        children.remove(0);
        children.remove(0);
        children.remove(0);
 
        children.add(five);
        children.add(six);
        two.setChildren(children);
        children.remove(0);
        children.remove(0);
 
        children.add(ten);
        children.add(eleven);
        four.setChildren(children);
        children.remove(0);
        children.remove(0);
 
        children.add(seven);
        children.add(eight);
        children.add(nine);
        six.setChildren(children);
        children.remove(0);
        children.remove(0);
        children.remove(0);
 
        children.add(twelve);
        ten.setChildren(children);
        children.remove(0);
 
        children.add(thirteen);
        children.add(fourteen);
        twelve.setChildren(children);
        children.remove(0);
        children.remove(0);
        //---------------------------------------------------------------------
 
        /***  DO NOT MAKE ANY CHANGE TO THE FOLLOWING CODE  ***/
        MyGenericTree<Integer> tree = new MyGenericTree<Integer>(root);
        tree.traverseInPostOrder();
    }
}
 
/***  DO NOT MAKE ANY CHANGE TO CLASS MyGenericTree EXCEPT THE PLACEHOLDER TO FILL IN  ***/
/***  YOU CANNOT ADD A NEW FIELD VARIABLE  ***/ 
/***  YOU CANNOT ADD A NEW METHOD DECLARATION  ***/ 
class MyGenericTree<T> {
    private TreeNode<T> root = null;
 
    public MyGenericTree(TreeNode<T> root) {
        this.root = root;
    }
 
    public void traverseInPostOrder() {
        traverseInPostOrder(root);
    }
 
    public void traverseInPostOrder(TreeNode<T> node) {     
        //---------------------------------------------------------------------
        System.out.println("1");
        while(node.children.front != null) {
            System.out.println(node.children.front);
            node.children.remove(0);
        }
        
        /*  
        if(node.children == null){
                System.out.print(node.data);
            }
            else{
                TreeNode curr = node.children.get(0);
                int i = 1;
                while(curr != null) {
                MyGenericTree<Integer> currNode = new MyGenericTree<Integer>(curr);
                //curr = node.children.get(i);
                currNode.traverseInPostOrder();
                //curr = curr.next;\
                i++;
            }
                System.out.print(node.data);
            }
            */
        //---------------------------------------------------------------------
    }
}
 
/***  DO NOT MAKE ANY CHANGE TO CLASS TreeNode  ***/
class TreeNode<N> {
    N data = null;
    TreeNode<N> parent = null;
    MyGenericLinkedList<TreeNode<N>> children = null;
 
    public TreeNode(N data) {
        this.data = data;
    }
 
    public void setChildren(MyGenericLinkedList<TreeNode<N>> children) {
        this.children = children;
    }
}
 
/***  DO NOT MAKE ANY CHANGE TO CLASS MyGenericLinkedList  ***/
class MyGenericLinkedList<S> {
    Node<S> front;
 
    public MyGenericLinkedList() {
        front = null;
    }
 
    public void add(S value) {
        if (front == null) {
            front = new Node<S>(value);
        } else {
            Node<S> current = front;
            while (current.next != null) {
                current = current.next;
            }
            current.next = new Node<S>(value);
        }
    }
 
    public S get(int index) {
        Node<S> current = front;
        for (int i = 0; i < index; i++) {
            current = current.next;
        }
        return (S)current.data;
    }
 
    public void remove(int index) {
        if (index == 0) {
            front = front.next;
        } else {
            Node<S> current = front;
            for (int i = 0; i < index - 1; i++) {
                current = current.next;
            }
            current.next = current.next.next;
        }
    }
}
 
/***  DO NOT MAKE ANY CHANGE TO CLASS Node  ***/
class Node<X> {
    X data;
    Node<X> next;
 
    public Node(X data) {
        this.data = data;
        this.next = null;
    }
 
    public Node(X data, Node<X> next) {
        this.data = data;
        this.next = next;
    }
}

Answer 1

根据您拥有迭代器的方式，在打印出来后可能会破坏链表。 通常，在使用链表时，您希望保留该列表。 下面是遍历链表的基本概念。

while(node.children.front != null) {
    System.out.println(node.children.front);
    node.children.front = node.children.front.next
}

在任何时候，您只能访问单个节点，因此如果您想转到下一个节点，则必须将当前节点设置为列表中的下一个。 由于它可能为空，这就是为什么您要条件检查节点是否设置为空值的原因。 如果它设置为空值，则您位于链表的末尾。