design-linked-list

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Algorithms

Design your implementation of the linked list. You can choose to use a singly or doubly linked list. 
A node in a singly linked list should have two attributes: <code>val</code> and <code>next</code>. <code>val</code> is the value of the current node, and <code>next</code> is a pointer/reference to the next node. 
If you want to use the doubly linked list, you will need one more attribute <code>prev</code> to indicate the previous node in the linked list. Assume all nodes in the linked list are 0-indexed.

Implement the <code>MyLinkedList</code> class:

<ul>
	<li><code>MyLinkedList()</code> Initializes the <code>MyLinkedList</code> object.</li>
	<li><code>int get(int index)</code> Get the value of the <code>indexth</code> node in the linked list. If the index is invalid, return <code>-1</code>.</li>
	<li><code>void addAtHead(int val)</code> Add a node of value <code>val</code> before the first element of the linked list. After the insertion, the new node will be the first node of the linked list.</li>
	<li><code>void addAtTail(int val)</code> Append a node of value <code>val</code> as the last element of the linked list.</li>
	<li><code>void addAtIndex(int index, int val)</code> Add a node of value <code>val</code> before the <code>indexth</code> node in the linked list. If <code>index</code> equals the length of the linked list, the node will be appended to the end of the linked list. If <code>index</code> is greater than the length, the node will not be inserted.</li>
	<li><code>void deleteAtIndex(int index)</code> Delete the <code>indexth</code> node in the linked list, if the index is valid.</li>
</ul>

&nbsp;
Example 1:

<pre>
Input
[&quot;MyLinkedList&quot;, &quot;addAtHead&quot;, &quot;addAtTail&quot;, &quot;addAtIndex&quot;, &quot;get&quot;, &quot;deleteAtIndex&quot;, &quot;get&quot;]
[[], [1], [3], [1, 2], [1], [1], [1]]
Output
[null, null, null, null, 2, null, 3]

Explanation
MyLinkedList myLinkedList = new MyLinkedList();
myLinkedList.addAtHead(1);
myLinkedList.addAtTail(3);
myLinkedList.addAtIndex(1, 2); // linked list becomes 1-&gt;2-&gt;3
myLinkedList.get(1); // return 2
myLinkedList.deleteAtIndex(1); // now the linked list is 1-&gt;3
myLinkedList.get(1); // return 3
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>0 &lt;= index, val &lt;= 1000</code></li>
	<li>Please do not use the built-in LinkedList library.</li>
	<li>At most <code>2000</code> calls will be made to <code>get</code>, <code>addAtHead</code>, <code>addAtTail</code>, <code>addAtIndex</code> and <code>deleteAtIndex</code>.</li>
</ul>

Design Linked List

Design Skiplist

design-skiplist

设计跳表

Design

Linked List

你可以选择使用单链表或者双链表，设计并实现自己的链表。

单链表中的节点应该具备两个属性：<code>val</code> 和 <code>next</code> 。<code>val</code> 是当前节点的值，<code>next</code> 是指向下一个节点的指针/引用。

如果是双向链表，则还需要属性&nbsp;<code>prev</code>&nbsp;以指示链表中的上一个节点。假设链表中的所有节点下标从 0 开始。

实现 <code>MyLinkedList</code> 类：

<ul>
	<li><code>MyLinkedList()</code> 初始化 <code>MyLinkedList</code> 对象。</li>
	<li><code>int get(int index)</code> 获取链表中下标为 <code>index</code> 的节点的值。如果下标无效，则返回 <code>-1</code> 。</li>
	<li><code>void addAtHead(int val)</code> 将一个值为 <code>val</code> 的节点插入到链表中第一个元素之前。在插入完成后，新节点会成为链表的第一个节点。</li>
	<li><code>void addAtTail(int val)</code> 将一个值为 <code>val</code> 的节点追加到链表中作为链表的最后一个元素。</li>
	<li><code>void addAtIndex(int index, int val)</code> 将一个值为 <code>val</code> 的节点插入到链表中下标为 <code>index</code> 的节点之前。如果 <code>index</code> 等于链表的长度，那么该节点会被追加到链表的末尾。如果 <code>index</code> 比长度更大，该节点将 不会插入 到链表中。</li>
	<li><code>void deleteAtIndex(int index)</code> 如果下标有效，则删除链表中下标为 <code>index</code> 的节点。</li>
</ul>

&nbsp;

示例：

<pre>
输入
["MyLinkedList", "addAtHead", "addAtTail", "addAtIndex", "get", "deleteAtIndex", "get"]
[[], [1], [3], [1, 2], [1], [1], [1]]
输出
[null, null, null, null, 2, null, 3]

解释
MyLinkedList myLinkedList = new MyLinkedList();
myLinkedList.addAtHead(1);
myLinkedList.addAtTail(3);
myLinkedList.addAtIndex(1, 2); // 链表变为 1-&gt;2-&gt;3
myLinkedList.get(1); // 返回 2
myLinkedList.deleteAtIndex(1); // 现在，链表变为 1-&gt;3
myLinkedList.get(1); // 返回 3
</pre>

&nbsp;

提示：

<ul>
	<li><code>0 &lt;= index, val &lt;= 1000</code></li>
	<li>请不要使用内置的 LinkedList 库。</li>
	<li>调用 <code>get</code>、<code>addAtHead</code>、<code>addAtTail</code>、<code>addAtIndex</code> 和 <code>deleteAtIndex</code> 的次数不超过 <code>2000</code> 。</li>
</ul>