findDecentNumber.js

function getDecentNumber(N) {

	let number = -1, 
        inc = 5,
        five_str = "5", 
        three_str = "3",
        five_num = 5, 
        three_num = 3;
    
    // numberCast function will turn any string up to 16 digits
    // into a number due to Javascript limitation on anything longer
    let numberCast = (n) => (n.length <= 16) ? Number(n) : n;
	
	if( N <= 2) { return number };
	
	if ( N % 5 === 0 ) {
		return numberCast(three_str.repeat(N));
	}
    
    if ( N % 3 === 0 ) {
		return numberCast(five_str.repeat(N));
	}
	while (inc < N) {
	 
	 if ( (inc % five_num) === 0 && ((N - inc) % three_num) === 0) {
		number = `${five_str.repeat(N - inc)}${three_str.repeat(inc)}`;
		break;
	 }
	
	 inc += five_num;
		
	}
	
	return numberCast(number);
}




// OLD - KEEPING WITH REFACTORED FOR REFERENCE
// function findDecentNumber(N) {
// 	var big = + Array(N).fill(5).join('');
// 	var number = -1;
// 	var count = 0, fives = N, threes = 0;
// 	var inc = 2, diff = 0, base = 0;
// 	if( N % 3 === 0) return big;
// 	while(count < N) {
// 		base = Math.pow(10, count);
// 		diff = 2 * base;
// 		big -= diff;
// 		fives -= 1;
// 		threes += 1;

// 		if( (fives % 3 === 0) && (threes % 5 === 0) ) {
// 			// exit and return number
// 			number = big;
// 			break;
// 		}
// 		count++;
// 	}
// 	return number;
// }