leecode 上的Design Linked List 用例59

• Z时代
• 2024-03-13
• 分类：IT

第59个用例无法通过，求解答。报错和对应代码位置如图。

class MyLinkedList {
    int length;
    Node head;
    class Node{
        int val;
        Node next;
        Node(int x){
            this.val = x;
        }
    }
    public MyLinkedList() {
        this.length = 0;
        this.head = null;
    }
    public int get(int index) {
        if(index < 0 || index >= this.length){
            return -1;
        }
        else {
            int counter = 0;
            Node curr = head;
            while(counter != (index)){
                curr = curr.next;
                counter++;
            }
            return curr.val;
        }
    }
    public void addAtHead(int val) {
        Node newNode = new Node(val);
        newNode.next = this.head;
        this.head = newNode;
        this.length++;    
    }
    public void addAtTail(int val) {
        if(this.length == 0){
            addAtHead(val);
            return;
        }
        Node newNode = new Node(val);
        Node temp = head;
        while(temp.next != null){
            temp = temp.next;
        }
        temp.next = newNode;
        newNode.next = null;
        this.length++;
    }
    public void addAtIndex(int index, int val) {
        Node newNode = new Node(val);
        Node temp = head;
        int counter = 0;
        if((index) == this.length){
            addAtTail(val);
            return;
        }
        if(index > this.length){
            return;
        }
        if(index == 0){
            addAtHead(val);
            return;
        }
        while(counter != (index-1)){
            temp = temp.next;
            counter++;
        }
        newNode.next = temp.next;
        temp.next = newNode;
        this.length++;
    }
    public void deleteAtIndex(int index) {
        if(index < 0 || index >= this.length){
            return;
        }
        Node curr = head;
        if(index == 0 ){
            head = curr.next;
        }
        else{
            Node current = head;
            Node pre = null;
            int counter = 0;
            while(counter != index){
                pre = current;
                current = current.next;
                counter++;
            }
            pre.next = current.next;
            this.length--;
        }
    }
}
/**
 * Your MyLinkedList object will be instantiated and called as such:
 * MyLinkedList obj = new MyLinkedList();
 * int param_1 = obj.get(index);
 * obj.addAtHead(val);
 * obj.addAtTail(val);
 * obj.addAtIndex(index,val);
 * obj.deleteAtIndex(index);
 */

回答：

    public void deleteAtIndex(int index) {
        // ...................
        Node curr = head;
        if(index == 0 ){
            head = curr.next;
            // !!!!! 这里没有修改 length 。然后 length 与链表的实际长度不匹配了。
            // !!!!! get 的时候又是根据 length 而不是链表的实际内容判断是否出界，然后就出错了。
        }
        else{
            // ...............
            this.length--;
        }

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