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https://github.com/dholerobin/Lecture_Notes.git
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200 lines
5.2 KiB
HTML
200 lines
5.2 KiB
HTML
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<html>
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<head>
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<style type="text/css">
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.container {
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position: static;
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width: 800px;
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height: 350px;
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overflow: hidden;
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}
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.embed {
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height: 100%;
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width: 100%;
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min-width: 1000px;
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margin-left: -360px;
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margin-top: -57px;
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overflow: hidden;
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}
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body {
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width: 800px;
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margin: auto;
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padding: 1em;
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font-family: "Open Sans", sans-serif;
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line-height: 150%;
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letter-spacing: 0.1pt;
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}
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img {
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width: 90%;
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text-align: center;
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margin: auto;
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box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
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}
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pre, code {
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padding: 1em;
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}
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</style>
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<script>
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document.addEventListener('readystatechange', event => {
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if (event.target.readyState === "complete")
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document.activeElement.blur();
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});
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</script>
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<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/styles/default.min.css">
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<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.1/highlight.min.js"></script>
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</head>
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<body>
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<h2 id="characterswithspecialmeaning">Characters with special meaning</h2>
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<p>We have seen that, we are using <code>*</code>, <code>+</code>, <code>.</code>, <code>$</code>, etc for different purposes. Now, if we want to match them themselves, we have to escape them using escape character(backslash-\) .</p>
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<p>Below is the table for these kind of characters and their escaped version, along with their usages.</p>
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<table>
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<tr>
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<td>Character</td>
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<td>Usage</td>
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<td>Escaped version</td>
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<td></td>
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</tr>
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<tr>
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<td>\</td>
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<td>escape character</td>
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<td>\\</td>
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<td></td>
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</tr>
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<tr>
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<td>.</td>
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<td>predefined character class</td>
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<td>\.</td>
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<td></td>
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</tr>
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<tr>
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<td>|</td>
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<td>OR operator</td>
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<td>\\</td>
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<td></td>
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</tr>
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<tr>
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<td>*</td>
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<td>as quantifier</td>
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<td>\*</td>
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<td></td>
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</tr>
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<tr>
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<td>+</td>
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<td>as quantifier</td>
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<td>\+</td>
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<td></td>
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</tr>
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<tr>
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<td>?</td>
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<td>as quantifier</td>
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<td>\?</td>
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<td></td>
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</tr>
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<tr>
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<td>^</td>
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<td>boundary matcher</td>
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<td>\^</td>
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<td></td>
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</tr>
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<tr>
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<td>$</td>
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<td>boundary matcher</td>
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<td>\$</td>
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<td></td>
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</tr>
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<tr>
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<td>{</td>
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<td>in quantifier notation</td>
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<td>\{</td>
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<td></td>
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</tr>
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<tr>
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<td>}</td>
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<td>in quantifier notation</td>
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<td>\}</td>
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<td></td>
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</tr>
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<tr>
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<td>[</td>
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<td>in character class notation</td>
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<td>\[</td>
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<td></td>
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</tr>
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<tr>
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<td>]</td>
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<td>in character class notation</td>
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<td>\]</td>
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<td></td>
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</tr>
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<tr>
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<td>(</td>
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<td>in group notation</td>
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<td>\(</td>
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<td></td>
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</tr>
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<tr>
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<td>)</td>
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<td>in group notation</td>
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<td>\)</td>
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<td></td>
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</tr>
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<tr>
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<td>-</td>
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<td>range operator</td>
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<td>NA</td>
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<td></td>
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</tr>
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</table>
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<p>Sometimes, it is also preferred to use escaped forward slash(<code>/</code>).</p>
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<h2 id="bonusproblems">Bonus Problems</h2>
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<ol>
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<li><p>Predict the output of the following regex:</p>
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<p><strong>RegEx:</strong> <code>\b(0|(1(01*0)*1))*\b</code> <br>
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<strong>Text:</strong> This RegEx denotes the set of binary numbers divisible by 3:
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0,11,1010, 1100, 1111, 1001</p>
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<p>Answer: </p>
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<div class="container">
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<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vtqu" class="embed"></iframe>
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</div></li>
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<li><p>Find a regular expression to match whole lines in the text containing either Apple, Orange, Grape as a word.</p>
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<p>Hint: Use <code>^</code> and <code>$</code> to match whole lines.</p>
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<p>Answer: <code>^.*\b(apple|orange|grape)\b.*$</code></p>
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<div class="container">
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<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vtra" class="embed"></iframe>
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</div></li>
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<li><p>Find an expression which matches <code>cat.</code>, <code>896.</code>, <code>?=++</code> but not <code>abc1</code>.</p>
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<p>Answer: <code>...\W</code></p>
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<div class="container">
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<iframe scrolling="no" style="position: absolute; top: -9999em; visibility: hidden;" onload="this.style.position='static'; this.style.visibility='visible';" src="https://regexr.com/4vu8e" class="embed"></iframe>
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</div></li>
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</ol>
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<script type="text/javascript">
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||
|
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document.addEventListener('DOMContentLoaded', (event) => {
|
||
|
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document.querySelectorAll('pre code').forEach((block) => {
|
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|
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hljs.highlightBlock(block);
|
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|
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});
|
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|
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});
|
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|
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</script>
|
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</body>
|
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</html>
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