feat: Solve linked list cycle detector

  - Hackerrank

Author: brianr482

detect-cycle-linked-list.js

@@ -0,0 +1,47 @@
+/**
+ * Hackerrank
+ *  A linked list is said to contain a cycle if any node is visited more than
+ * once while traversing the list. Complete the function provided for you in
+ * your editor. It has one parameter: a pointer to a Node object named  that
+ * points to the head of a linked list. Your function must return a boolean
+ * denoting whether or not there is a cycle in the list. If there is a cycle,
+ * return true; otherwise, return false.
+ * 
+ * Constraints:
+ * 1. 0 <= list size <= 1000
+ * 
+ * This solution got 5 points
+ * Problem link: http://hr.gs/ffddcc
+ */
+
+/*
+ * For your reference:
+ *
+ * SinglyLinkedListNode {
+ *     int data;
+ *     SinglyLinkedListNode next;
+ * }
+ *
+ */
+
+/**
+ * @param {SinglyLinkedListNode} head The root of the linked list
+ * @return {boolean} If there's a cycle in the linked list
+ */
+function hasCycle(head) {
+  // Edge case
+  if (!head) {
+    return false;
+  }
+  const visited = new Set();
+  let node = head;
+  while (node) {
+    if (visited.has(node)) {
+      return true;
+    } else {
+      visited.add(node);
+    }
+    node = node.next;
+  }
+  return false;
+}