add: 链表的中间节点

src/list/middle-of-the-linked-list.js

@@ -0,0 +1,25 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+export const middleNode = function (head) {
+  if (!head.next) return head
+  if (head.next && !head.next.next) return head.next
+
+  let slow = head
+  let fast = head.next.next
+
+  while (fast.next && fast.next.next) {
+    slow = slow.next
+    fast = fast.next.next
+  }
+
+  return fast.next ? slow.next.next : slow.next
+}