add leetcode problem-cn part6

算法题（国内版）/problem (Chinese)/反转链表 [reverse-linked-list].html

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+给你单链表的头节点 <code>head</code> ，请你反转链表，并返回反转后的链表。
+<div class="original__bRMd">
+<div>
+<p> </p>
+
+<p><strong>示例 1：</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/rev1ex1.jpg" style="width: 542px; height: 222px;" />
+<pre>
+<strong>输入：</strong>head = [1,2,3,4,5]
+<strong>输出：</strong>[5,4,3,2,1]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2021/02/19/rev1ex2.jpg" style="width: 182px; height: 222px;" />
+<pre>
+<strong>输入：</strong>head = [1,2]
+<strong>输出：</strong>[2,1]
+</pre>
+
+<p><strong>示例 3：</strong></p>
+
+<pre>
+<strong>输入：</strong>head = []
+<strong>输出：</strong>[]
+</pre>
+
+<p> </p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li>链表中节点的数目范围是 <code>[0, 5000]</code></li>
+	<li><code>-5000 <= Node.val <= 5000</code></li>
+</ul>
+
+<p> </p>
+
+<p><strong>进阶：</strong>链表可以选用迭代或递归方式完成反转。你能否用两种方法解决这道题？</p>
+</div>
+</div>