Added linked list cycle solution

Author: nhistory

linked-list-cycle/nhistory.js

@@ -0,0 +1,24 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+
+/**
+ * @param {ListNode} head
+ * @return {boolean}
+ */
+var hasCycle = function (head) {
+  // Make fast pointer
+  // Fast pointer will move two steps further inside of list
+  let fast = head;
+  // Iterate until fast pointer and head is equal
+  while (fast && fast.next) {
+    head = head.next;
+    fast = fast.next.next;
+    if (head == fast) return true;
+  }
+  return false;
+};