add: 链表的中间节点

test/list/ListNode.js

@@ -0,0 +1,17 @@
+export default class ListNode {
+  constructor (val) {
+    this.val = val
+    this.next = null
+  }
+}
+
+export 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
+}