ts-4: address review comments (import, ditch extra type def)

Author: aikhelis

typescript/Fast and Slow Pointers/linked_list_loop.ts

@@ -1,14 +1,15 @@
-/* Definition of ListNode: 
+import { ListNode } from "./ds";
+
+/* Definition of ListNode:
 class ListNode {
     val: number; next: ListNode | null;
     constructor(val: number) {
         this.val = val;
         this.next = null;
     }
-}    
-*/
+}*/
 
-function linkedListLoop(head: ListNode): boolean {
+function linkedListLoop(head: ListNode | null): boolean {
     let slow: ListNode | null = head;
     let fast: ListNode | null = head;
     // Check both 'fast' and 'fast.next' to avoid null pointer

typescript/Fast and Slow Pointers/linked_list_loop_naive.ts

@@ -1,14 +1,16 @@
+import { ListNode } from "./ds";
+
 /* Definition of ListNode:
 class ListNode {
     val: number; next: ListNode | null;
     constructor(val: number) {
         this.val = val;
         this.next = null;
     }
-}    
-*/
+}*/
+
 
-function linkedListLoopNaive(head: ListNode): boolean {
+function linkedListLoopNaive(head: ListNode | null): boolean {
     const visited: Set<ListNode> = new Set();
     let curr: ListNode | null = head;
     while (curr !== null) {

typescript/Fast and Slow Pointers/linked_list_midpoint.ts

@@ -1,15 +1,16 @@
-/* Definition of ListNode: 
+import { ListNode } from "./ds";
+
+/* Definition of ListNode:
 class ListNode {
     val: number; next: ListNode | null;
     constructor(val: number) {
         this.val = val;
         this.next = null;
     }
-}    
-*/
+}*/
 
 
-function linkedListMidpoint(head: ListNode): ListNode | null {
+function linkedListMidpoint(head: ListNode | null): ListNode | null {
     let slow: ListNode | null = head;
     let fast: ListNode | null = head;
     // When the fast pointer reaches the end of the list, the slow