Add solution #142

Author: JoshCrozier

README.md

@@ -75,6 +75,7 @@
 133|[Clone Graph](./0133-clone-graph.js)|Medium|
 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|
 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/0142-linked-list-cycle-ii.js

@@ -0,0 +1,39 @@
+/**
+ * 142. Linked List Cycle II
+ * https://leetcode.com/problems/linked-list-cycle-ii/
+ * Difficulty: Medium
+ *
+ * Given the head of a linked list, return the node where the cycle begins.
+ * If there is no cycle, return null.
+ *
+ * There is a cycle in a linked list if there is some node in the list that
+ * can be reached again by continuously following the next pointer. Internally,
+ * pos is used to denote the index of the node that tail's next pointer is
+ * connected to (0-indexed). It is -1 if there is no cycle. Note that pos is
+ * not passed as a parameter.
+ *
+ * Do not modify the linked list.
+ */
+
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+var detectCycle = function(head) {
+  while (head) {
+    if (head.visited) {
+      return head;
+    }
+    head.visited = 1;
+    head = head.next;
+  }
+  return head;
+};