24. 两两交换链表中的节点

Author: w2xi

README.md

@@ -21,6 +21,7 @@
 |14|[最长公共前缀](https://leetcode-cn.com/problems/longest-common-prefix/)|[JavaScript](./algorithms/longest-common-prefix.js)|Easy|
 |20|[有效的括号](https://leetcode.cn/problems/valid-parentheses/)|[JavaScript](./algorithms/valid-parentheses.js)|Easy|
 |21|[合并两个有序链表](https://leetcode-cn.com/problems/merge-two-sorted-lists/)|[JavaScript](./algorithms/merge-two-sorted-lists.js)|Easy|
+|24|[两两交换链表中的节点](https://leetcode.cn/problems/swap-nodes-in-pairs/)|[JavaScript](./algorithms/swap-nodes-in-pairs.js)|Medium|
 |26|[删除有序数组中的重复项](https://leetcode.cn/problems/remove-duplicates-from-sorted-array/)|[JavaScript](./algorithms/remove-duplicates-from-sorted-array.js)|Easy|
 |27|[移除元素](https://leetcode.cn/problems/remove-element/)|[JavaScript](./algorithms/remove-element.js)|Easy|
 |28|[实现 strStr()](https://leetcode-cn.com/problems/implement-strstr/)|[JavaScript](./algorithms/implement-strstr.js)|Easy|

algorithms/swap-nodes-in-pairs.js

@@ -0,0 +1,29 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var swapPairs = function (head) {
+  if (!head || !head.next) return head;
+  let dummyNode = new ListNode(-1);
+  dummyNode.next = head;
+  let prev = dummyNode;
+  let curr = head;
+
+  while (curr && curr.next) {
+    const temp = curr.next.next;
+    prev.next = curr.next;
+    curr.next.next = curr;
+    curr.next = temp;
+    prev = curr;
+    curr = temp;
+  }
+
+  return dummyNode.next;
+};