From 10853399368ce28ee6b38f412d9da5cbe94546f3 Mon Sep 17 00:00:00 2001
From: CyC2018 <1029579233@qq.com>
Date: Fri, 6 Apr 2018 16:43:06 +0800
Subject: [PATCH] auto commit

---
 notes/算法.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/notes/算法.md b/notes/算法.md
index 2ddd1f1b..27fb7023 100644
--- a/notes/算法.md
+++ b/notes/算法.md
@@ -301,10 +301,12 @@ public class Queue<Item> {
     }
 
     // 出队列
-    public Item dequeue(){
+    public Item dequeue() {
+        if (isEmpty()) return null;
         Node node = first;
         first = first.next;
         N--;
+        if (isEmpty()) last = null;
         return node.item;
     }
 }