JavaScript factorial prevent infinity
Question
I have been using this function for calculating factorial numbers in JavaScript:
var f = [];
function factorial (n) {
if (n == 0 || n == 1)
return 1;
if (f[n] > 0)
return f[n];
return f[n] = factorial(n-1) * n;
}
All seemed to be going well until I tried the number 500 . It returned infinity .
Is there a way that I can prevent infinity as an answer?
Thank you.
5 answers
solution1
7 ACCPTED 2014-01-15 10:07:19
You indeed need to use bignumbers. With math.js you can do:
// configure math.js to work with enough precision to do our calculation
math.config({precision: 2000});
// evaluate the factorial using a bignumber value
var value = math.bignumber(500);
var result = math.factorial(value);
// output the results
console.log(math.format(result, {notation: 'fixed'}));
This will output:
solution2
2 2014-01-14 23:45:55
500! is, for lack of a better term, "[bleep]ing huge".
It is far, far beyond what can be stored in a double-precision float, which is what JavaScript uses for numbers.
There's no way to prevent this, other than use numbers that are reasonable :p
EDIT: To show you just how huge it is, here's the answer:
500! =
That right there is a 1,135-digit number. For comparison, double-precision floats can handle about 15 digits of precision.
solution3
1 2014-01-14 23:48:43
You could consider using an arbitrary precision numeric library. This is a question of its own, though. Here's one related question: https://stackoverflow.com/questions/744099/is-there-a-good-javascript-bigdecimal-library .
solution4
1 2014-06-07 06:58:01
I dont know if anyone has solved this elsewise... I'm a novice beginner in coding and dont know all the aspects. But after I faced this factorial problem myself, i came here when searching for the answer. I solved the 'infinity' display problem in another way. I dont know if its very efficient or not. But it does show the results of even verry high intergers.
Sorry for any redundancy or untidiness in the code.
<!DOCTYPE html>
<html>
<head>
<title>Factorial</title>
<script src='http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js'></script>
</head>
<body>
<input type='text' id='number' />
<input type='button' value='!Factorial!' id='btn' />
<script>
var reslt=1;
var counter=0;
var mantissa=0; //stores the seperated matissa
var exponent=0; //stores the seperated exponent
$(document).ready(function (){
$('#btn').click(function (){
var num=parseFloat($('#number').val()); //number input by user
for(i=1;i<=num;i++){
reslt=reslt*i;
//when the result becomes so high that the exponent reaches 306, the number is divided by 1e300
if((parseFloat(reslt.toExponential().toString().split("e")[1]))>=300){
reslt=reslt/1e300; //the result becomes small again to be able to be iterated without becoming infinity
counter+=1; //the number of times that the number is divided in such manner is recorded by counter
}
}
//the mantissa of the final result is seperated first
mantissa=parseFloat(reslt.toExponential().toString().split("e")[0]);
//the exponent of the final result is obtained by adding the remaining exponent with the previously dropped exponents (1e300)
exponent=parseFloat(reslt.toExponential().toString().split("e")[1])+300*counter;
alert(mantissa+"e+"+exponent); //displays the result as a string by concatenating
//resets the variables and fields for the next input if any
$('#number').val('');
reslt=1;
mantissa=0;
exponent=0;
counter=0;
});
});
</script>
</body>
</html>
solution5
0 2021-06-16 22:46:43
Javascript numbers can only get so big before they just become "Infinity". If you want to support bigger numbers, you'll have to use BigInt .
Examples:
// Without BigInt console.log(100 ** 1000) // Infinity // With BigInt // (stackOverflow doesn't seem to print the result, // unless I turn it into a string first) console.log(String(100n ** 1000n)) // A really big number
So, for your specific bit of code, all you need to do is turn your numeric literals into BigInt literals, like this:
var f = []; function factorial (n) { if (n == 0n || n == 1n) return 1n; if (f[n] > 0n) return f[n]; return f[n] = factorial(n-1n) * n; } console.log(String(factorial(500n)));
You'll find that you computer can run that piece of code in a snap.
solution6
-4 2014-01-14 23:42:12
Some improves in your code
function factorial (n) {
if (n === 0 || n === 1)
return 1;
return factorial(n-1) * n;
}
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