add: 环形链表

test/list/linked-list-cycle.test.js

@@ -0,0 +1,24 @@
+import { hasCycle } from '../../src/list/linked-list-cycle'
+
+function ListNode (val) {
+  this.val = val
+  this.next = null
+}
+
+const arrToList = (arr) => {
+  const head = new ListNode(arr[0])
+  let current = head
+  for (let n = 1, len = arr.length; n < len; n++) {
+    current.next = new ListNode(arr[n])
+    current = current.next
+  }
+
+  return head
+}
+
+test('环形链表', () => {
+  const list = arrToList([1, 2, 3])
+  list.next.next.next = list
+  expect(hasCycle(list)).toBe(true)
+  expect(hasCycle(arrToList([1, 2, 3]))).toBe(false)
+})