JavaScript/Project-Euler/Problem004.js at master · ArduinoAficionado/JavaScript · GitHub

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// https://projecteuler.net/problem=4

/* A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

export const largestPalindromic = (digits) => {

let i

let n

let m

let d

let limit

let number = 0

for (i = 1; i < digits; i++) {

number = 10 * number + 9

}

const inf = number // highest (digits - 1) number, in this example highest 2 digit number

const sup = 10 * number + 9 // highest (digits) number, in this example highest 3 digit number

const isPalindromic = (n) => {

let p = 0

const q = n

let r

while (n > 0) {

r = n % 10

p = 10 * p + r

n = Math.floor(n / 10)

}

return p === q // returning whether the number is palindromic or not

}

for (n = sup * sup, m = inf * inf; n > m; n--) {

if (isPalindromic(n)) {

limit = Math.ceil(Math.sqrt(n))

d = sup

while (d >= limit) {

if (n % d === 0 && n / d > inf) {

return n

}

d -= 1

}

return NaN // returning not a number, if any such case arise

}

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