BE AWARE working solution in this post
Questions
Object/2-dimensional array dilemma
Not directly related to working solution, but in earlier versions of code was 2 options:
Use nested array or Use object for {key:value} format.
What logic can be applied when making such decisions?
Naming options
In the code below there is function
getProductOfAllPrimeDivisors
This name refers to the mathematical nature of function.
Alternative would be
generateLoopStep
This name refers to the implementation specifics.
What is the best practice when choosing between these two options.
Terminal condition
In this solution I used for loop with empty terminal condition. I could easily set relevant terminal condition. But I decided not to.
Main reason - I can prove by math definitions that in my case terminal condition isn’t necessary at all.
But I still have a suspicion - maybe it’s not best practice?
Any feedback in general would be appreciated.
//factorial is definitely multiple of numbers from 1 to n
//UNIT 1:factorial(n)
//input: number output: number
const factorial = (num) => { //??? maybe there are built-in functions for factorial, more efficient
//base case
if (num === 0 || num === 1) {
return 1;
}
//recursive step
else {
return num * factorial(num - 1);
}
}
//if we factorize(factorial(n)) => can get array of its prime divisors
//we will be searching for smallestMult with loop,
//BUT it will be loop with VERY WIDE step
//for the test case smallestMult(5) answer is 60, but loop step will be 30(2*3*5)
//for the test case smallestMult(13) answer is 360360, but loop step will be 30030(!!!!!!)
//we know(from experiments/testing) >>> factorial and smallestMult
//have the same prime divisors
//loop step will be >>> product of all prime divisors of factorial
//technically it will be nested loops
//BUT >>> the bigger size of problem >>> the wider will be loop step
//UNIT(2) getProductOFAllPrimeDivisors(n) //alternative func name generateLoopStep
//input: number output: number
const getProductOfAllPrimeDivisors = (num) => {
let result = 1;
const arrayOfDivisors = []; //need product of only one occurance
//of each prime divisor
while (num !== 1) {
for (let i = 2; i <= num; i++) {
if (num % i === 0) {
num = num / i; //need to reinit.num even if primefactor is a duplicate
if (arrayOfDivisors.indexOf(i) == -1){
//accumulating only if its 1st occurance of prime factor
result *= i;
arrayOfDivisors.push(i);
}
break;
}
}
}
return result;
}
//unit testing
/*
console.log(getProductOfAllPrimeDivisors(120));//30
console.log(getProductOfAllPrimeDivisors(2520));//210
console.log(getProductOfAllPrimeDivisors(24));//6
console.log(getProductOfAllPrimeDivisors(360360));//30030
*/
//UNIT for solution
function smallestMult(n) {
const loopStep = getProductOfAllPrimeDivisors(factorial(n));
for (let i = loopStep;;i+=loopStep) { //can set terminal condition but from math standpoint it makes no sense
for (let j = 1; j <= n; j++) { //lets loop through all divisors >>> can be optimized using array from UNIT2
if (i % j !== 0) { //check not passed>>>get out of inner loop
break;
}
//if we on final iter. step and all checks passed >>> job done
if (n === j) {
return i;
}
}
}
}
//fCC test passed