Add solution #143

Author: JoshCrozier

README.md

@@ -77,6 +77,7 @@
 136|[Single Number](./0136-single-number.js)|Easy|
 141|[Linked List Cycle](./0141-linked-list-cycle.js)|Easy|
 142|[Linked List Cycle II](./0142-linked-list-cycle-ii.js)|Medium|
+143|[Reorder List](./0143-reorder-list.js)|Medium|
 144|[Binary Tree Preorder Traversal](./0144-binary-tree-preorder-traversal.js)|Easy|
 145|[Binary Tree Postorder Traversal](./0145-binary-tree-postorder-traversal.js)|Easy|
 151|[Reverse Words in a String](./0151-reverse-words-in-a-string.js)|Medium|

solutions/0143-reorder-list.js

@@ -0,0 +1,57 @@
+/**
+ * 143. Reorder List
+ * https://leetcode.com/problems/reorder-list/
+ * Difficulty: Medium
+ *
+ * You are given the head of a singly linked-list. The list can be represented as:
+ *
+ * L0 → L1 → … → Ln - 1 → Ln
+ * Reorder the list to be on the following form:
+ *
+ * L0 → Ln → L1 → Ln - 1 → L2 → Ln - 2 → …
+ * You may not modify the values in the list's nodes. 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 {void} Do not return anything, modify head in-place instead.
+ */
+var reorderList = function(head) {
+  if (!head || !head.next || !head.next.next) {
+    return head;
+  }
+
+  let list1 = head;
+  let list2 = head;
+
+  while (list2.next && list2.next.next) {
+    list1 = list1.next;
+    list2 = list2.next.next;
+  }
+
+  let center1 = list1;
+  let center2 = list1.next;
+  while (center2.next) {
+    const temp = center2.next;
+    center2.next = temp.next;
+    temp.next = center1.next;
+    center1.next = temp;
+  }
+
+  list1 = head;
+  list2 = center1.next;
+  while (list1 != center1) {
+    center1.next = list2.next;
+    list2.next = list1.next;
+    list1.next = list2;
+    list1 = list2.next;
+    list2 = center1.next;
+  }
+};