add: 二叉树的层序遍历

test/tree/binary-tree-level-order-traversal.test.js

@@ -0,0 +1,11 @@
+import { levelOrder } from '../../src/tree/binary-tree-level-order-traversal'
+import Tree from './Tree.js'
+
+test('二叉树的层序遍历', () => {
+  const source = [3, 9, 20, null, null, 15, 7]
+  expect(levelOrder(Tree.arrToTree(source))).toEqual([
+    [3],
+    [9, 20],
+    [15, 7]
+  ])
+})