Add linked-list-cycle solution in TS

Author: Jeehay28

linked-list-cycle/Jeehay28.ts

@@ -0,0 +1,52 @@
+class ListNode {
+  val: number;
+  next: ListNode | null;
+  constructor(val?: number, next?: ListNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.next = next === undefined ? null : next;
+  }
+}
+
+// TC: O(n)
+// SC: O(1)
+function hasCycle(head: ListNode | null): boolean {
+
+  let fast: ListNode | null = head;
+  let slow: ListNode | null = head;
+
+  while (fast && fast.next) {
+    fast = fast.next.next;
+
+    if (slow !== null) {
+      slow = slow.next;
+    } else {
+      return false;
+    }
+
+    if (fast === slow) return true;
+  }
+
+  return false;
+}
+
+
+// TC: O(n)
+// SC: O(n)
+/*
+function hasCycle(head: ListNode | null): boolean {
+
+  let dummy: ListNode | null = head;
+  const visited = new Set<ListNode>();
+
+  while (dummy) {
+    if (visited.has(dummy)) return true;
+
+    visited.add(dummy);
+
+    dummy = dummy.next;
+  }
+
+  return false;
+}
+*/
+