Add solution #24

Author: JoshCrozier

README.md

@@ -25,6 +25,7 @@
 20|[Valid Parentheses](./0020-valid-parentheses.js)|Easy|
 21|[Merge Two Sorted Lists](./0021-merge-two-sorted-lists.js)|Easy|
 22|[Generate Parentheses](./0022-generate-parentheses.js)|Medium|
+24|[Swap Nodes in Pairs](./0024-swap-nodes-in-pairs.js)|Medium|
 27|[Remove Element](./0027-remove-element.js)|Easy|
 28|[Implement strStr()](./0028-implement-strstr.js)|Easy|
 31|[Next Permutation](./0031-next-permutation.js)|Medium|

solutions/0024-swap-nodes-in-pairs.js

@@ -0,0 +1,31 @@
+/**
+ * 24. Swap Nodes in Pairs
+ * https://leetcode.com/problems/swap-nodes-in-pairs/
+ * Difficulty: Medium
+ *
+ * Given a linked list, swap every two adjacent nodes and return its head. You must solve the
+ * problem without modifying the values in the list's nodes (i.e., only nodes themselves may
+ * be changed.)
+ */
+
+/**
+ * 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;
+
+  const result = head.next;
+  head.next = result.next;
+  result.next = head;
+  head.next = swapPairs(head.next);
+
+  return result;
+};