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chore: Merge pull request #745 from lvlte/ProjectEuler/016

Project Euler - Problem 16

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`195`	`195`	`* [Problem013](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem013.js)`
`196`	`196`	`* [Problem014](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem014.js)`
`197`	`197`	`* [Problem015](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem015.js)`
	`198`	`+ * [Problem016](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem016.js)`
`198`	`199`	`* [Problem020](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem020.js)`
`199`	`200`	`* [Problem1](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem1.js)`
`200`	`201`	`* [Problem10](https://github.com/TheAlgorithms/Javascript/blob/master/Project-Euler/Problem10.js)`

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	`1`	`+/**`
	`2`	`+ * Problem 16 - Power digit sum`
	`3`	`+ *`
	`4`	`+ * @see {@link https://projecteuler.net/problem=16}`
	`5`	`+ *`
	`6`	`+ * 215 = 32768 and the sum of its digits is 3 +たす 2 +たす 7 +たす 6 +たす 8 =わ 26.`
	`7`	`+ *`
	`8`	`+ * What is the sum of the digits of the number 21000 ?`
	`9`	`+ */`
	`10`	`+`
	`11`	`+/**`
	`12`	`+ * Returns the power digit sum of n^pow.`
	`13`	`+ *`
	`14`	`+ * @param {number} [n=2]`
	`15`	`+ * @param {number} [pow=1000]`
	`16`	`+ * @returns {number}`
	`17`	`+ */`
	`18`	`+const powerDigitSum = function (n = 2, pow = 1000) {`
	`19`	`+ // The idea is to consider each digit (d*10^exp) separately, right-to-left.`
	`20`	`+ // digits = [units, tens, ...]`
	`21`	`+`
	`22`	`+ const digits = [n]`
	`23`	`+ let p = 1`
	`24`	`+`
	`25`	`+ while (++p <= pow) {`
	`26`	`+ let carry = 0`
	`27`	`+ for (let exp = 0; exp < digits.length; exp++) {`
	`28`	`+ const prod = digits[exp] * n + carry`
	`29`	`+ carry = Math.floor(prod / 10)`
	`30`	`+ digits[exp] = prod % 10`
	`31`	`+ }`
	`32`	`+ while (carry > 0) {`
	`33`	`+ digits.push(carry % 10)`
	`34`	`+ carry = Math.floor(carry / 10)`
	`35`	`+ }`
	`36`	`+ }`
	`37`	`+`
	`38`	`+ // (digits are reversed but we only want the sum so it doesn't matter)`
	`39`	`+`
	`40`	`+ return digits.reduce((prev, current) => prev + current, 0)`
	`41`	`+}`
	`42`	`+`
	`43`	`+export { powerDigitSum }`

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	`1`	`+import { powerDigitSum } from '../Problem016'`
	`2`	`+`
	`3`	`+describe('Check Problem 16 - Power digit sum', () => {`
	`4`	`+ it('Power digit sum of 2^15', () => {`
	`5`	`+ expect(powerDigitSum(2, 15)).toBe(26)`
	`6`	`+ })`
	`7`	`+`
	`8`	`+ it('Power digit sum of 2^1000', () => {`
	`9`	`+ expect(powerDigitSum()).toBe(1366)`
	`10`	`+ expect(powerDigitSum(2, 1000)).toBe(1366)`
	`11`	`+ })`
	`12`	`+`
	`13`	`+ it('Power digit sum of 3^5000', () => {`
	`14`	`+ expect(powerDigitSum(3, 5000)).toBe(11097)`
	`15`	`+ })`
	`16`	`+})`

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