diff --git a/src/main/java/leetcode/editor/cn/MergeTwoSortedLists.java b/src/main/java/leetcode/editor/cn/MergeTwoSortedLists.java
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+//将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 
+//
+// 
+//
+// 示例 1： 
+//
+// 
+//输入：l1 = [1,2,4], l2 = [1,3,4]
+//输出：[1,1,2,3,4,4]
+// 
+//
+// 示例 2： 
+//
+// 
+//输入：l1 = [], l2 = []
+//输出：[]
+// 
+//
+// 示例 3： 
+//
+// 
+//输入：l1 = [], l2 = [0]
+//输出：[0]
+// 
+//
+// 
+//
+// 提示： 
+//
+// 
+// 两个链表的节点数目范围是 [0, 50] 
+// -100 <= Node.val <= 100 
+// l1 和 l2 均按 非递减顺序 排列 
+// 
+// Related Topics 递归 链表 
+// 👍 1744 👎 0
+
+package leetcode.editor.cn;
+
+import com.code.leet.entiy.ListNode;
+
+//21:合并两个有序链表
+public class MergeTwoSortedLists{
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new MergeTwoSortedLists().new Solution();
+    }
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        if (l1 == null) {
+            return l2;
+        }
+        if (l2 == null) {
+            return l1;
+        }
+        if (l1.val < l2.val) {
+            l1.next = mergeTwoLists(l1.next, l2);
+            return l1;
+        } else {
+            l2.next = mergeTwoLists(l1, l2.next);
+            return l2;
+        }
+    }
+}
+//leetcode submit region end(Prohibit modification and deletion)
+
+}
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diff --git a/src/main/java/leetcode/editor/cn/MergeTwoSortedLists.md b/src/main/java/leetcode/editor/cn/MergeTwoSortedLists.md
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+<p>将两个升序链表合并为一个新的 <strong>升序</strong> 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 </p>
+
+<p> </p>
+
+<p><strong>示例 1：</strong></p>
+<img alt="" src="https://assets.leetcode.com/uploads/2020/10/03/merge_ex1.jpg" style="width: 662px; height: 302px;" />
+<pre>
+<strong>输入：</strong>l1 = [1,2,4], l2 = [1,3,4]
+<strong>输出：</strong>[1,1,2,3,4,4]
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<pre>
+<strong>输入：</strong>l1 = [], l2 = []
+<strong>输出：</strong>[]
+</pre>
+
+<p><strong>示例 3：</strong></p>
+
+<pre>
+<strong>输入：</strong>l1 = [], l2 = [0]
+<strong>输出：</strong>[0]
+</pre>
+
+<p> </p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li>两个链表的节点数目范围是 <code>[0, 50]</code></li>
+	<li><code>-100 <= Node.val <= 100</code></li>
+	<li><code>l1</code> 和 <code>l2</code> 均按 <strong>非递减顺序</strong> 排列</li>
+</ul>
+<div><div>Related Topics</div><div><li>递归</li><li>链表</li></div></div>\n<div><li>👍 1744</li><li>👎 0</li></div>
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