update: 二叉树的层序遍历

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

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([])
 })