Add 206 reverse linked list

typescript/src/206-reverse-linked-list.ts

@@ -0,0 +1,40 @@
+// Definition for singly-linked list.
+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
+  }
+}
+
+/**
+ * Problem: https://leetcode.com/problems/reverse-linked-list/
+ * @param head - linked list
+ * @returns reversed linked list
+ */
+export function reverseList(head: ListNode | null): ListNode | null {
+  if (head == null || head.next == null) return head
+
+  const last = reverseList(head.next)
+  head.next.next = head
+  head.next = null
+  return last
+}
+
+if (import.meta.vitest) {
+  const { test, expect } = import.meta.vitest
+  test('test one', () => {
+    expect(
+      reverseList(
+        new ListNode(1, new ListNode(2, new ListNode(3, new ListNode(4))))
+      )
+    ).toStrictEqual(
+      new ListNode(4, new ListNode(3, new ListNode(2, new ListNode(1))))
+    )
+  })
+
+  test('test two', () => {
+    expect(reverseList(new ListNode(1))).toStrictEqual(new ListNode(1))
+  })
+}