跟读练习: Heaps in 3 minutes — Intro - 通过视频学习英语口语
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Today we're going to learn about heaps.
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You'll often hear the word heap when discussing storage for garbage collection in languages such as Java,
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but this video is about the heap data structure that is used to manage information.
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Heaps are sometimes called binary heaps and are nearly complete binary trees.
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Here's an example of a heap.
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By a nearly complete binary tree, I mean that all levels are filled except the lowest,
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and the lowest level is filled up to a certain point starting from the left.
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Uses of heaps include heap sort and priority queues.
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And there are two kinds of heaps, max heaps and min heaps.
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On the left we have a max heap.
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The condition for a max heap is
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that the value of the node i is less than or equal to the value of its parent.
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Max heaps are used for heap sort.
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Similarly, for the min heap, the value of the node i is greater than or equal to the value of its parent.
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min heaps are great for priority queues.
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Because we said heaps are nearly complete binary trees, we know that the height of a heap is O of log n,
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which you'll see in various operations that we'll learn later.
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I'd also like to show heaps represented as an array.
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Here's our max heap and here it is as an array.
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The root of the tree is at index 1 of the array.
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To get a node's left child, you simply take the index times by 2.
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And to get the node's right child, you take the index times by 2 and add 1.
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Finally, to retrieve a node's parent is the floor of the node's index divided by 2.
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We choose to put the root at index 1 instead of 0,
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as it keeps this arithmetic cleaner and most computers can do these operations with fewer instructions.
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Let's take a look at 15, which is at index 3.
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The left child of 15 is equal to 2 times 3 which is the sixth index and a node value of 12.
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The right child of 15 is 2 times 3 plus 1 which is the index of 7 or the node 13.
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Lastly, the parent of 15 is the floor of 3 divided by 2, which is the first index and the root of our tree, 21.
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You know I prefer brevity, so we'll end the video here
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and in the next one I'll show you how to create a heap from an unordered array.
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本课的词汇与口语要点
这节口语课以视频“Heaps in 3 minutes — Intro”为素材。 视频中反复出现的词有：heap, index, max, tree, value。 这段视频共有 5 个句子、409 个单词可供跟读。 讲话部分时长为 3:28。 说话人语速平稳，每分钟约 118 个词，很适合跟读。 只有 79% 的单词属于英语最常用的 3,000 词，词汇难度较高。
视频中的重点词汇
视频中 12 个值得学习的单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| binary 形容词 | /ˈbaɪ.nə.ɹi/ | 二進 /二进 |
| node 名词 | /noʊd/ | 結節 /结节 |
| priority 名词 | /pɹaɪˈɒɹɪti/ | 優先權 /优先权, 更重要的事 |
| divide 动词 | /dɪˈvaɪd/ | 分, 分裂 |
| sixth 形容词 | /sɪksθ/ | 第六 |
| fewer | /ˈfjuː.ɚ/ | 較少 /较少, 更少 |
| similarly 副词 | /ˈsɪm.ə.lə.li/ | 類似地 /类似地, 同樣地 /同样地 |
| garbage 名词 | /ˈɡɑɹ.bɪd͡ʒ/ | 垃圾, 廢物 /废物 |
| instruction 名词 | /ɪnˈstɹʌkʃən/ | 教導 /教导 |
| queue 名词 | /kju/ | 隊列 /队列 |
| retrieve 动词 | /ɹɪˈtɹiːv/ | 重拾 |
| arithmetic 名词 | /æɹɪθˈmɛtɪk/ | 算術 /算术 |
需要注意的发音
说话人用了 6 次缩略和弱读形式，例如 we'll, I'd, I'll。请按听到的简短形式来说。
- “th” 音: sixth /sɪksθ/, arithmetic /æɹɪθˈmɛtɪk/
- 长单词——注意重音位置: priority /pɹaɪˈɒɹɪti/, similarly /ˈsɪm.ə.lə.li/, arithmetic /æɹɪθˈmɛtɪk/
中文母语者容易读错的音：
- /v/ — 不要读成 /w/，上齿轻触下唇: divide /dɪˈvaɪd/, java /ˈd͡ʒɑː.və/, retrieve /ɹɪˈtɹiːv/, brevity /ˈbɹɛvɪti/
- 词尾辅音 — 要读清楚，后面不要加元音: node /noʊd/, divide /dɪˈvaɪd/, sixth /sɪksθ/, garbage /ˈɡɑɹ.bɪd͡ʒ/, retrieve /ɹɪˈtɹiːv/
- /æ/ — 嘴张大，不要读成 /e/: lastly /ˈlæstli/, arithmetic /æɹɪθˈmɛtɪk/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 用正常速度逐句跟读，每句重复到你的节奏与说话人一致为止。
- 录下自己的声音并与原声对比，特别注意 binary, node, priority 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。