Problem 37

function isPrime(number) {

if (number === 1) {return false}

const threshold = Math.ceil(Math.sqrt(number));

for (let i = threshold; i > 1; i--) {

if (number % i === 0 ) {

return false;

}

}

return true;

}

function arrayToNumber(inputArr) {

return inputArr.reduce((a,b, index) => a + b * 10 ** (inputArr.length - 1 - index), 0)

}

function giveTruncatedPrimes(inputArr) {

const elegibleNumbers = [1,3,5,7,9]

if (inputArr.length === 1000000) {return []}

const outputArr = [];

if (!isPrime(arrayToNumber(inputArr)) ) {

return [];

}

outputArr.push(inputArr)

for (let i of elegibleNumbers) {

outputArr.push(...giveTruncatedPrimes([i, ...inputArr]))

}

// console.log(inputArr, ' --- ', outputArr)

// console.log(inputArr, ' --- ', outputArr.filter(x => isPrime(arrayToNumber(x.slice(x.length - inputArr.length)))))

// console.log(inputArr, ' --- ', outputArr.map(x => x.slice( 0, (x.length - inputArr.length)) ))

const filterFunction = (x) => isPrime(arrayToNumber(x.slice(0, x.length - inputArr.length + 1 )))

return outputArr.filter(filterFunction).filter(x => x.length > 1)

}

console.log(giveTruncatedPrimes([]).map(arrayToNumber))

// console.log(giveTruncatedPrimes([]).map(arrayToNumber).reduce((a, b) => a + b, 0))