From 7ff3a150b742619b951aa6f2d23558afb9f39d90 Mon Sep 17 00:00:00 2001
From: yi-ge <a@wyr.me>
Date: Wed, 13 May 2020 13:58:11 +0800
Subject: [PATCH] =?UTF-8?q?update:=20=E4=BA=8C=E5=8F=89=E6=A0=91=E7=9A=84?=
 =?UTF-8?q?=E5=B1=82=E5=BA=8F=E9=81=8D=E5=8E=86?=
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---
 src/tree/binary-tree-level-order-traversal.js       | 8 ++++----
 test/tree/binary-tree-level-order-traversal.test.js | 3 +++
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/tree/binary-tree-level-order-traversal.js b/src/tree/binary-tree-level-order-traversal.js
index bc4d46b..dae06bd 100644
--- a/src/tree/binary-tree-level-order-traversal.js
+++ b/src/tree/binary-tree-level-order-traversal.js
@@ -17,11 +17,11 @@ export const levelOrder = function (root) {
     const leave = queue.length // 记录这一层有几个
     for (let i = 0; i < leave; i++) { // 一次性把固定个数的队列执行完
       const node = queue.shift()
-      if (node.left) queue.push(node.left)
-      if (node.right) queue.push(node.right)
-      tmp.push(node.val)
+      if (node && node.left) queue.push(node.left)
+      if (node && node.right) queue.push(node.right)
+      if (node) tmp.push(node.val)
     }
-    res.push(tmp)
+    if (tmp.length) res.push(tmp)
   }
 
   return res
diff --git a/test/tree/binary-tree-level-order-traversal.test.js b/test/tree/binary-tree-level-order-traversal.test.js
index 208093f..6bba858 100644
--- a/test/tree/binary-tree-level-order-traversal.test.js
+++ b/test/tree/binary-tree-level-order-traversal.test.js
@@ -8,4 +8,7 @@ test('二叉树的层序遍历', () => {
     [9, 20],
     [15, 7]
   ])
+
+  const source1 = []
+  expect(levelOrder(Tree.arrToTree(source1))).toEqual([])
 })