115 lines
2.0 KiB
Markdown
115 lines
2.0 KiB
Markdown
|
---
|
||
|
|
id: 5d79253307ecd49e030bdcd1
|
||
|
|
title: Step 23
|
||
|
|
challengeType: 0
|
||
|
|
dashedName: step-23
|
||
|
|
---
|
||
|
|
|
||
|
|
# --description--
|
||
|
|
|
||
|
|
Recursion is when a function calls itself. We often use it instead of `while`/`for` loops, as loops usually involve mutable state.
|
||
|
|
|
||
|
|
Replace the empty string in `highPrecedence` with a call to `highPrecedence` with `str2` as argument.
|
||
|
|
|
||
|
|
# --hints--
|
||
|
|
|
||
|
|
See description above for instructions.
|
||
|
|
|
||
|
|
```js
|
||
|
|
assert(
|
||
|
|
highPrecedence('2*2*2') === '8' &&
|
||
|
|
highPrecedence('2*2') === '4' &&
|
||
|
|
highPrecedence('2+2') === '2+2'
|
||
|
|
);
|
||
|
|
```
|
||
|
|
|
||
|
|
# --seed--
|
||
|
|
|
||
|
|
## --before-user-code--
|
||
|
|
|
||
|
|
```html
|
||
|
|
<!DOCTYPE html>
|
||
|
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<meta charset="UTF-8">
|
||
|
|
<title>Spreadsheet</title>
|
||
|
|
<style>
|
||
|
|
#container {
|
||
|
|
display: grid;
|
||
|
|
grid-template-columns: 50px repeat(10, 200px);
|
||
|
|
grid-template-rows: repeat(11, 30px);
|
||
|
|
}
|
||
|
|
.label {
|
||
|
|
background-color: lightgray;
|
||
|
|
text-align: center;
|
||
|
|
vertical-align: middle;
|
||
|
|
line-height: 30px;
|
||
|
|
}
|
||
|
|
</style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div id="container">
|
||
|
|
<div></div>
|
||
|
|
</div>
|
||
|
|
```
|
||
|
|
|
||
|
|
## --after-user-code--
|
||
|
|
|
||
|
|
```html
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
```
|
||
|
|
|
||
|
|
## --seed-contents--
|
||
|
|
|
||
|
|
```html
|
||
|
|
<script>
|
||
|
|
|
||
|
|
const infixToFunction = {
|
||
|
|
"+": (x, y) => x + y,
|
||
|
|
"-": (x, y) => x - y,
|
||
|
|
"*": (x, y) => x * y,
|
||
|
|
"/": (x, y) => x / y
|
||
|
|
};
|
||
|
|
|
||
|
|
const infixEval = (str, regex) =>
|
||
|
|
str.replace(regex, (_, arg1, fn, arg2) =>
|
||
|
|
infixToFunction[fn](parseFloat(arg1), parseFloat(arg2))
|
||
|
|
);
|
||
|
|
|
||
|
|
--fcc-editable-region--
|
||
|
|
const highPrecedence = str => {
|
||
|
|
const regex = /([0-9.]+)([*\/])([0-9.]+)/;
|
||
|
|
const str2 = infixEval(str, regex);
|
||
|
|
return str === str2 ? str : "";
|
||
|
|
};
|
||
|
|
--fcc-editable-region--
|
||
|
|
|
||
|
|
|
||
|
|
</script>
|
||
|
|
```
|
||
|
|
|
||
|
|
# --solutions--
|
||
|
|
|
||
|
|
```html
|
||
|
|
<script>
|
||
|
|
const infixToFunction = {
|
||
|
|
"+": (x, y) => x + y,
|
||
|
|
"-": (x, y) => x - y,
|
||
|
|
"*": (x, y) => x * y,
|
||
|
|
"/": (x, y) => x / y
|
||
|
|
};
|
||
|
|
|
||
|
|
const infixEval = (str, regex) =>
|
||
|
|
str.replace(regex, (_, arg1, fn, arg2) =>
|
||
|
|
infixToFunction[fn](parseFloat(arg1), parseFloat(arg2))
|
||
|
|
);
|
||
|
|
|
||
|
|
const highPrecedence = str => {
|
||
|
|
const regex = /([0-9.]+)([*\/])([0-9.]+)/;
|
||
|
|
const str2 = infixEval(str, regex);
|
||
|
|
return str === str2 ? str : highPrecedence(str2);
|
||
|
|
};
|
||
|
|
</script>
|
||
|
|
```
|