107 lines
3.5 KiB
Markdown
107 lines
3.5 KiB
Markdown
---
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title: GeneratorExponential
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id: 5a23c84252665b21eecc7e7b
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challengeType: 5
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---
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## Description
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<section id='description'>
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A generator is an executable entity (like a function or procedure) that contains code that yields a sequence of values, one at a time, so that each time you call the generator, the next value in the sequence is provided.
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Generators are often built on top of coroutines or objects so that the internal state of the object is handled “naturally”.
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Generators are often used in situations where a sequence is potentially infinite, and where it is possible to construct the next value of the sequence with only minimal state.
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Write a function that uses generators to generate squares and cubes. Create a new generator that filters all cubes from the generator of squares.
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The function should return the \( n^{th} \) value of the filtered generator.
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For example for \(n=7\), the function should return 81 as the sequence would be 4,9,16,25,36,49,81. Here 64 is filtered out, as it is a cube.
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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: '''<code>exponentialGenerator</code> should be a function.'''
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testString: 'assert(typeof exponentialGenerator==''function'',''<code>exponentialGenerator</code> should be a function.'');'
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- text: '''<code>exponentialGenerator()</code> should return a number.'''
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testString: 'assert(typeof exponentialGenerator(10)==''number'',''<code>exponentialGenerator()</code> should return a number.'');'
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- text: '''<code>exponentialGenerator(10)</code> should return <code>144</code>.'''
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testString: 'assert.equal(exponentialGenerator(10),144,''<code>exponentialGenerator(10)</code> should return <code>144</code>.'');'
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- text: '''<code>exponentialGenerator(12)</code> should return <code>196</code>.'''
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testString: 'assert.equal(exponentialGenerator(12),196,''<code>exponentialGenerator(12)</code> should return <code>196</code>.'');'
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- text: '''<code>exponentialGenerator(14)</code> should return <code>256</code>.'''
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testString: 'assert.equal(exponentialGenerator(14),256,''<code>exponentialGenerator(14)</code> should return <code>256</code>.'');'
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- text: '''<code>exponentialGenerator(20)</code> should return <code>484</code>.'''
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testString: 'assert.equal(exponentialGenerator(20),484,''<code>exponentialGenerator(20)</code> should return <code>484</code>.'');'
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- text: '''<code>exponentialGenerator(25)</code> should return <code>784</code>.'''
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testString: 'assert.equal(exponentialGenerator(25),784,''<code>exponentialGenerator(25)</code> should return <code>784</code>.'');'
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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='js-seed'>
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```js
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function exponentialGenerator (n) {
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// Good luck!
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}
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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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```js
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function exponentialGenerator(n){
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function* PowersGenerator(m) {
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var n=0;
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while(1) {
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yield Math.pow(n, m);
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n += 1;
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}
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}
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function* FilteredGenerator(g, f){
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var value = g.next().value;
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var filter = f.next().value;
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while(1) {
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if( value < filter ) {
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yield value;
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value = g.next().value;
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} else if ( value > filter ) {
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filter = f.next().value;
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} else {
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value = g.next().value;
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filter = f.next().value;
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}
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}
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}
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var squares = PowersGenerator(2);
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var cubes = PowersGenerator(3);
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var filtered = FilteredGenerator(squares, cubes);
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var curr=0;
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for(var i=0;i<n;i++) curr=filtered.next();
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return curr.value;
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}
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```
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</section>
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