87 lines
6.8 KiB
Markdown
87 lines
6.8 KiB
Markdown
---
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id: 587d8257367417b2b2512c7e
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title: Use Depth First Search in a Binary Search Tree
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challengeType: 1
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videoUrl: ''
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localeTitle: 在二叉搜索树中使用深度优先搜索
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---
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## Description
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<section id="description">我们知道如何在二叉搜索树中搜索特定值。但是,如果我们只想探索整棵树呢?或者,如果我们没有有序树,我们只需要搜索一个值?这里我们将介绍一些可用于探索树数据结构的树遍历方法。首先是深度优先搜索。在深度优先搜索中,在搜索继续到另一个子树之前,尽可能深地探索给定子树。有三种方法可以完成:按顺序:从最左边的节点开始搜索,到最右边的节点结束。预购:在树叶前探索所有的根。下订单:在根之前探索所有的叶子。您可能会猜到,您可以选择不同的搜索方法,具体取决于树存储的数据类型以及您要查找的内容。对于二叉搜索树,inorder遍历以排序顺序返回节点。说明:这里我们将在二叉搜索树上创建这三种搜索方法。深度优先搜索是一种固有的递归操作,只要子节点存在,它就会继续探索更多的子树。一旦理解了这个基本概念,您就可以简单地重新排列探索节点和子树的顺序,以生成上述三个搜索中的任何一个。例如,在后序搜索中,我们希望在开始返回任何节点本身之前一直递归到叶节点,而在预订搜索中,我们希望首先返回节点,然后继续递归在树下。在我们的树上定义<code>inorder</code> , <code>preorder</code>和<code>postorder</code>方法。这些方法中的每一个都应该返回表示树遍历的项数组。确保返回数组中每个节点的整数值,而不是节点本身。最后,如果树为空,则返回<code>null</code> 。 </section>
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## Instructions
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<section id="instructions">
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: 存在<code>BinarySearchTree</code>数据结构。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() }; return (typeof test == "object")})(), "The <code>BinarySearchTree</code> data structure exists.");'
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- text: 二叉搜索树有一个名为<code>inorder</code>的方法。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; return (typeof test.inorder == "function")})(), "The binary search tree has a method called <code>inorder</code>.");'
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- text: 二叉搜索树有一个名为<code>preorder</code>的方法。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; return (typeof test.preorder == "function")})(), "The binary search tree has a method called <code>preorder</code>.");'
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- text: 二叉搜索树有一个名为<code>postorder</code>的方法。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; return (typeof test.postorder == "function")})(), "The binary search tree has a method called <code>postorder</code>.");'
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- text: <code>inorder</code>方法返回由inorder遍历产生的节点值数组。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; if (typeof test.inorder !== "function") { return false; }; test.add(7); test.add(1); test.add(9); test.add(0); test.add(3); test.add(8); test.add(10); test.add(2); test.add(5); test.add(4); test.add(6); return (test.inorder().join("") == "012345678910"); })(), "The <code>inorder</code> method returns an array of the node values that result from an inorder traversal.");'
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- text: <code>preorder</code>方法返回由前序遍历产生的节点值数组。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; if (typeof test.preorder !== "function") { return false; }; test.add(7); test.add(1); test.add(9); test.add(0); test.add(3); test.add(8); test.add(10); test.add(2); test.add(5); test.add(4); test.add(6); return (test.preorder().join("") == "710325469810"); })(), "The <code>preorder</code> method returns an array of the node values that result from a preorder traversal.");'
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- text: <code>postorder</code>方法返回由后序遍历产生的节点值数组。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; if (typeof test.postorder !== "function") { return false; }; test.add(7); test.add(1); test.add(9); test.add(0); test.add(3); test.add(8); test.add(10); test.add(2); test.add(5); test.add(4); test.add(6); return (test.postorder().join("") == "024653181097"); })(), "The <code>postorder</code> method returns an array of the node values that result from a postorder traversal.");'
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- text: <code>inorder</code>方法为空树返回<code>null</code> 。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; if (typeof test.inorder !== "function") { return false; }; return (test.inorder() == null); })(), "The <code>inorder</code> method returns <code>null</code> for an empty tree.");'
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- text: <code>preorder</code>方法为空树返回<code>null</code> 。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; if (typeof test.preorder !== "function") { return false; }; return (test.preorder() == null); })(), "The <code>preorder</code> method returns <code>null</code> for an empty tree.");'
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- text: <code>postorder</code>方法为空树返回<code>null</code> 。
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testString: 'assert((function() { var test = false; if (typeof BinarySearchTree !== "undefined") { test = new BinarySearchTree() } else { return false; }; if (typeof test.postorder !== "function") { return false; }; return (test.postorder() == null); })(), "The <code>postorder</code> method returns <code>null</code> for an empty tree.");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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var displayTree = (tree) => console.log(JSON.stringify(tree, null, 2));
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function Node(value) {
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this.value = value;
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this.left = null;
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this.right = null;
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}
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function BinarySearchTree() {
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this.root = null;
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// change code below this line
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// change code above this line
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}
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```
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</div>
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### After Test
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<div id='js-teardown'>
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```js
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console.info('after the test');
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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