123 lines
2.1 KiB
Markdown
123 lines
2.1 KiB
Markdown
---
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id: 5900f3ab1000cf542c50febe
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title: 'Problem 63: Powerful digit counts'
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challengeType: 5
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forumTopicId: 302175
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dashedName: problem-63-powerful-digit-counts
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---
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# --description--
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The 5-digit number, 16807 = 7<sup>5</sup>, is also a fifth power. Similarly, the 9-digit number, 134217728 = 8<sup>9</sup>, is a ninth power.
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Complete the function so that it returns how many positive integers are of length `n` and an `n`th power.
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# --hints--
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`powerfulDigitCounts(1)` should return a number.
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```js
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assert(typeof powerfulDigitCounts(1) === 'number');
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```
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`powerfulDigitCounts(1)` should return `9`.
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```js
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assert.strictEqual(powerfulDigitCounts(1), 9);
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```
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`powerfulDigitCounts(2)` should return `6`.
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```js
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assert.strictEqual(powerfulDigitCounts(2), 6);
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```
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`powerfulDigitCounts(3)` should return `5`.
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```js
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assert.strictEqual(powerfulDigitCounts(3), 5);
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```
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`powerfulDigitCounts(4)` should return `4`.
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```js
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assert.strictEqual(powerfulDigitCounts(4), 4);
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```
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`powerfulDigitCounts(5)` should return `3`.
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```js
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assert.strictEqual(powerfulDigitCounts(5), 3);
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```
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`powerfulDigitCounts(6)` should return `3`.
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```js
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assert.strictEqual(powerfulDigitCounts(6), 3);
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```
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`powerfulDigitCounts(7)` should return `2`.
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```js
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assert.strictEqual(powerfulDigitCounts(7), 2);
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```
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`powerfulDigitCounts(8)` should return `2`.
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```js
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assert.strictEqual(powerfulDigitCounts(8), 2);
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```
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`powerfulDigitCounts(10)` should return `2`.
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```js
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assert.strictEqual(powerfulDigitCounts(10), 2);
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```
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`powerfulDigitCounts(21)` should return `1`.
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```js
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assert.strictEqual(powerfulDigitCounts(21), 1);
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```
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# --seed--
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## --seed-contents--
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```js
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function powerfulDigitCounts(n) {
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return true;
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}
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powerfulDigitCounts(1);
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```
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# --solutions--
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```js
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function powerfulDigitCounts(n) {
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function countDigits(num) {
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let counter = 0;
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while (num > 0) {
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num = Math.floor(num / 10);
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counter++;
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}
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return counter;
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}
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let numbersCount = 0;
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let curNum = 1;
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while (curNum < 10) {
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let power = n;
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if (power === countDigits(curNum ** power)) {
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numbersCount++;
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}
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curNum++;
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}
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return numbersCount;
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}
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```
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