2019-11-05 02:09:40 -01:00
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---
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id: 5d79253307ecd49e030bdcd1
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2019-12-09 19:37:02 +09:00
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title: Part 023
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2019-11-05 02:09:40 -01:00
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challengeType: 0
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2020-06-24 16:22:14 +09:00
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isHidden: true
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2019-11-05 02:09:40 -01:00
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---
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## Description
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<section id='description'>
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2019-12-09 19:37:02 +09:00
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Recursion is when a function calls itself. We often use it instead of `while`/`for` loops, as loops usually involve mutable state.
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2019-11-05 02:09:40 -01:00
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Replace the empty string in `highPrecedence` with a call to `highPrecedence` with `str2` as argument.
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</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: See description above for instructions.
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testString: assert(highPrecedence("2*2*2") === "8" && highPrecedence("2*2") === "4" && highPrecedence("2+2") === "2+2");
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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='html-seed'>
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```html
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<script>
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const infixToFunction = {
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"+": (x, y) => x + y,
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"-": (x, y) => x - y,
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"*": (x, y) => x * y,
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"/": (x, y) => x / y
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};
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const infixEval = (str, regex) =>
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str.replace(regex, (_, arg1, fn, arg2) =>
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infixToFunction[fn](parseFloat(arg1), parseFloat(arg2))
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);
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const highPrecedence = str => {
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const regex = /([0-9.]+)([*\/])([0-9.]+)/;
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const str2 = infixEval(str, regex);
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return str === str2 ? str : "";
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};
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</script>
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```
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</div>
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### Before Test
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<div id='html-setup'>
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>Spreadsheet</title>
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<style>
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#container {
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display: grid;
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grid-template-columns: 50px repeat(10, 200px);
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grid-template-rows: repeat(11, 30px);
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}
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.label {
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background-color: lightgray;
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text-align: center;
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vertical-align: middle;
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line-height: 30px;
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}
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</style>
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</head>
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<body>
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<div id="container">
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<div></div>
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</div>
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```
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</div>
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### After Test
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<div id='html-teardown'>
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```html
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</body>
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</html>
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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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```html
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<script>
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const infixToFunction = {
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"+": (x, y) => x + y,
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"-": (x, y) => x - y,
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"*": (x, y) => x * y,
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"/": (x, y) => x / y
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};
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const infixEval = (str, regex) =>
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str.replace(regex, (_, arg1, fn, arg2) =>
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infixToFunction[fn](parseFloat(arg1), parseFloat(arg2))
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);
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const highPrecedence = str => {
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const regex = /([0-9.]+)([*\/])([0-9.]+)/;
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const str2 = infixEval(str, regex);
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return str === str2 ? str : highPrecedence(str2);
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};
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</script>
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```
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</section>
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