Javascript代码改进-整数阶乘

Question

I am learning to code with Javascript and one exercise is about returning the factorial of a provided integer. For example: 5! = 1 * 2 * 3 * 4 * 5 = 120

I came up with a result and it was accepted. However, I am not so sure it would be the most efficient way of solving this.

Anyone would have any tips on how to improve this code?

function factorialize(num) {
    var array = [];  
    for (i = 1; i <= num; i++) {
        array.push(i);
    }
    var multi = 1;
    for (var i = 1; i < array.length; i++) {
        multi *= array[i];
    }
    return multi;
} 

Many thanks!!

Answer 1

You have several approaches to get a solution.

1. by iteration

    function f(n) { var r = n; while (--n) { r *= n; } return r; } 

2. by recursion

    function f(n) { return n === 0 ? 1 : n * f(n - 1); } 

   or a very short version

    function f(n) { return +!~-n || n * f(n - 1); } 

Answer 2

Why don't you use

var ans=1;
for (i=1;i<=num;i++)//for(i=num;i>=1;i--)
{
    ans=ans*i;
}
return ans;

Answer 3

I have used this kind of recursive method

function f(p) {
    if (p==1) return;
    p -= 1;
    x = x * p;
    f(p);        
}

A corrected version (with comments) :

function f(p) {
    if (p == 0) return 1;    /* 0! == 1 by definition,    */
    return p * f(p - 1);     /* otherwise p! = p * (p-1)! */
}