add solution for leetcode 024

Author: swiftwind0405

README.md

@@ -388,7 +388,7 @@ LeetCode
 |27|[Remove Element](https://leetcode.com/problems/remove-element/)| [js](./algorithms/removeElement/removeElement.js) [python](./algorithms/removeElement/removeElement.python) |Easy|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)|  [java](./algorithms/removeDuplicatesFromSortedArray/Solution.java)  |Easy|
 |25|[Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/)| |Hard|
-|24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)| |Medium|
+|24|[Swap Nodes in Pairs](https://leetcode.com/problems/swap-nodes-in-pairs/)| [js](./algorithms/swapNodesInPairs/swapNodesInPairs.js) |Medium|
 |23|[Merge k Sorted Lists](https://leetcode.com/problems/merge-k-sorted-lists/)| |Hard|
 |22|[Generate Parentheses](https://leetcode.com/problems/generate-parentheses/)| [js](./algorithms/generateParentheses/generateParentheses.js) |Medium|
 |21|[Merge Two Sorted Lists](https://leetcode.com/problems/merge-two-sorted-lists/)| |Easy|

algorithms/swapNodesInPairs/swapNodesInPairs.js

@@ -0,0 +1,14 @@
+var swapPairs = function(head) {
+    let shaob = new ListNode(0); // 添加哨兵 加0
+    shaob.next = head;
+    let shao = shaob;   //shao 是为了一直往下指, 而 shaob 其实是为了返回第二个节点
+    while(shao.next != null && shao.next.next != null) {
+        let start = shao.next; // 代表第一次的1
+        let end = shao.next.next; // 代表第一次的2
+        shao.next = end; // 0 指向 2
+        start.next = end.next; // 1 指向 3
+        end.next = start; // 2 指向 1
+        shao = start; // 将此时的1 也就是交换后的1当哨兵 继续循环
+    }
+    return shaob.next // 返回的是最初哨兵的前一个 就是链表头
+};