171 lines
3.6 KiB
Markdown
171 lines
3.6 KiB
Markdown
---
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id: 5d7925341747ad42b12f8e68
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title: Step 42
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challengeType: 0
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dashedName: step-42
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---
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# --description--
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This is still valid because we're modifying `arr` in place instead of reassigning to it (which is invalid with the `const` keyword). But doing this still modifies state, and we don't want to do that in functional programming.
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The `concat` method returns a new array instead of modifying an existing one:
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```js
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[1,2,3].concat(4); // [1, 2, 3, 4]
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[1,2,3].concat(4, 5); // [1, 2, 3, 4, 5]
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```
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Use `concat` instead of `push` to return the result of adding `end` to `arr`.
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# --hints--
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See description above for instructions.
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```js
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assert(
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JSON.stringify(range(1, 2)) === '[1,2]' &&
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code.includes('concat') &&
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!code.includes('push')
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);
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```
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# --seed--
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## --before-user-code--
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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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## --after-user-code--
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```html
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</body>
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</html>
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```
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## --seed-contents--
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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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const spreadsheetFunctions = {
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"": x => x
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};
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const applyFn = str => {
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const noHigh = highPrecedence(str);
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const infix = /([0-9.]+)([+-])([0-9.]+)/;
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const str2 = infixEval(noHigh, infix);
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const regex = /([a-z]*)\(([0-9., ]*)\)(?!.*\()/i;
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const toNumberList = args => args.split(",").map(parseFloat);
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const applyFunction = (fn, args) =>
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spreadsheetFunctions[fn.toLowerCase()](toNumberList(args));
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return str2.replace(
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regex,
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(match, fn, args) =>
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spreadsheetFunctions.hasOwnProperty(fn.toLowerCase()) ? applyFunction(fn, args) : match
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);
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};
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--fcc-editable-region--
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const range = (start, end) => {
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const arr = [start];
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arr.push(end);
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return arr;
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}
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--fcc-editable-region--
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</script>
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```
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# --solutions--
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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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const spreadsheetFunctions = {
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"": x => x
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};
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const applyFn = str => {
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const noHigh = highPrecedence(str);
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const infix = /([0-9.]+)([+-])([0-9.]+)/;
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const str2 = infixEval(noHigh, infix);
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const regex = /([a-z]*)\(([0-9., ]*)\)(?!.*\()/i;
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const toNumberList = args => args.split(",").map(parseFloat);
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const applyFunction = (fn, args) =>
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spreadsheetFunctions[fn.toLowerCase()](toNumberList(args));
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return str2.replace(
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regex,
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(match, fn, args) =>
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spreadsheetFunctions.hasOwnProperty(fn.toLowerCase()) ? applyFunction(fn, args) : match
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);
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};
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const range = (start, end) => {
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const arr = [start];
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return arr.concat(end);
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}
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</script>
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```
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