90 lines
1.5 KiB
Markdown
90 lines
1.5 KiB
Markdown
---
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id: 5900f37d1000cf542c50fe8f
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challengeType: 5
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title: 'Problem 16: Power digit sum'
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---
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## Description
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<section id='description'>
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2<sup>15</sup> = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.
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What is the sum of the digits of the number 2<sup><code>exponent</code></sup>?
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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>powerDigitSum(15)</code> should return 26.
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testString: assert.strictEqual(powerDigitSum(15), 26);
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- text: <code>powerDigitSum(128)</code> should return 166.
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testString: assert.strictEqual(powerDigitSum(128), 166);
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- text: <code>powerDigitSum(1000)</code> should return 1366.
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testString: assert.strictEqual(powerDigitSum(1000), 1366);
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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 powerDigitSum(exponent) {
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// Good luck!
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return true;
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}
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powerDigitSum(15);
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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 powerDigitSum(exponent) {
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const bigNum = [1];
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let sum = 0;
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for (let i = 1; i <= exponent; i++) {
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let count = bigNum.length + 1;
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let overflow = 0;
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for (let j = 0; j < count; j++) {
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let digit = bigNum[j] || 0;
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digit = 2 * digit + overflow;
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if (digit > 9) {
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digit -= 10;
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overflow = 1;
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} else {
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overflow = 0;
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}
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bigNum[j] = digit;
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}
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}
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bigNum.forEach(function(num) {
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return sum += num;
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});
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return sum;
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}
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```
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</section>
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