add 1721

fishercoder1534 · fishercoder1534 · commit 70e28b6d341a · 2021-01-09T20:40:27.000-08:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1721|[Swapping Nodes in a Linked List](https://leetcode.com/problems/swapping-nodes-in-a-linked-list/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1721.java) ||Medium|LinkedList|
 |1720|[Decode XORed Array](https://leetcode.com/problems/decode-xored-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1720.java) ||Easy|Bit Manipulation|
 |1718|[Construct the Lexicographically Largest Valid Sequence](https://leetcode.com/problems/construct-the-lexicographically-largest-valid-sequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1718.java) ||Medium|Backtracking, Recursion|
 |1716|[Calculate Money in Leetcode Bank](https://leetcode.com/problems/calculate-money-in-leetcode-bank/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1716.java) ||Easy|Math, Greedy|
diff --git a/src/main/java/com/fishercoder/solutions/_1721.java b/src/main/java/com/fishercoder/solutions/_1721.java
@@ -0,0 +1,33 @@
+package com.fishercoder.solutions;
+
+import com.fishercoder.common.classes.ListNode;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class _1721 {
+    public static class Solution1 {
+        public ListNode swapNodes(ListNode head, int k) {
+            List<Integer> list = new ArrayList<>();
+            ListNode tmp = head;
+            while (tmp != null) {
+                list.add(tmp.val);
+                tmp = tmp.next;
+            }
+            int first = list.get(k - 1);
+            int size = list.size();
+            int second = list.get(size - k);
+            list.remove(k - 1);
+            list.add(k - 1, second);
+            list.remove(size - k);
+            list.add(size - k, first);
+            ListNode pre = new ListNode(-1);
+            tmp = pre;
+            for (int i = 0; i < list.size(); i++) {
+                pre.next = new ListNode(list.get(i));
+                pre = pre.next;
+            }
+            return tmp.next;
+        }
+    }
+}
