在这里,我们走了!

首先,你为什么需要写这句话?

Math.divide = function(a,b)
{
    return a/b;
}

我会完全放弃。

您也可清理<条码>。 a 略微:

Math.factorial = function(n)
{
    n = Number(n);

    if (isNAN(n)) {
        alert("Factorial requires a numeric argument.");
        return null;
    } else if (n < 2) {
        return 1;
    } else {
        return (n * Math.factorial(n - 1));
    }
}

但主要问题是:<条码>():

onclick="var n = T1.value; var r = T2.value; var n_minus_r = parseFloat(n) - parseFloat(r); var numerator = Math.factorial(T1.value); var n_minus_r_fact = Math.factorial(n_minus_r); var r_fact = Math.factorial(r); var denominator = n_minus_r_fact * r_fact; T3.value = Math.divide(numerator,denominator); return true;

页: 1 d) 使它成为一种功能,并使它与这个要素相联,从而在你的超文本中消除所有强奸行为,使之更容易与以下方面合作:

window.onload = function()
{
    document.getElementById( calculate ).onclick = function() {
        var n = T1.value,
            r = T2.value;

        T3.value = Math.factorial(n) / (Math.factorial(r) * Math.factorial(n - r));
    }
}

仅删除<代码>onclick=。

If you re concerned about efficiency, you d probably want to re-implement the factorial as an iterative function rather than a recursive one. The recursive version will use a lot more memory and CPU time than the iterative version.

function factorial(n) { 
  var x=1; 
  var f=1;
  while (x<=n) {
    f*=x; x++;
  }
    return f;
}

You also shouldn t be adding your own functions to the Math namespace. It s not a good habit to get into.

As we know, combinations is short for(https://en.wikipedia.org/wiki/Combination):

So the fastest combinations implement is below(only if n is small):

// r*(r-1)*...*2*1
function factorial(r) {
  let s = 1;
  while (r > 1) s *= r--;
  return s;
}

function combinations(n,r){
    let s = 1;
    let i = r;
    // n*(n-1)*....*(n-r+1)
    while(i<n) s*=++i;
    return s/factorial(n-r)
}
console.log(combinations(100,2) === 4950) // false

Note: math float operation has Precision limit, for example combinations(100,2)==4950 is false. But https://www.wolframalpha.com/input?i=100+choose+2 tells us it s true result is 4950.

因此,我们应当使用<条码>BigInt取代<条码>float 业务:

// r*(r-1)*...*2*1
function factorial(r) {
    let s = BigInt(1);
    var i = BigInt(r)
    while (i > 1) s *= i--;
    return s;
}

// n*(n-1)*....*(n-r+1) / factorial(r)
function combinations(n, r){
    let s = BigInt(1);
    let i = BigInt(r);
    while(i<n) s*=++i;
    return s/factorial(n-r)
}
console.log(combinations(100,2) === 4950n) // true

Math.factorial= function(n){
    var i= n;
    while(--i) n*= i;
    return n;
}

Math.combinations= function(n, r, repeats){
    if(n< r) return 0;
    if(n=== r) return 1;
    if(repeats){
        return Math.factorial(n+r-1)/((Math.factorial(r)*Math.factorial(n-1)));
    }
    return Math.factorial(n)/((Math.factorial(r)*Math.factorial(n-r)));
}


var a= [
     aqua ,  black ,  blue ,  fuchsia ,  gray ,  green ,  lime ,  maroon ,
     navy ,  olive ,  orange ,  purple ,  red ,  silver ,  teal ,  white ,
     yellow 
]
//how many 3 color combinations are there?
//[red,green,blue] is different than [green,red,blue]
// Math.combinations(a.length,3,true) >>969
// how many unique combinations (ignoring order) are there?
// Math.combinations(a.length,3)>>680

我更喜欢休养功能,尾补假可能会造成诸如菲博托等职能的停滞。

Math._factorial = function(n){
  return Math._fact(n,1);
}

Math._fact= function(n,res){
  n = Number(n);
  if (n == null) {
    alert("Factorial requires a numeric argument.");
    return null;
  } else if (n < 2){
    return res;
  } else {
    return Math._fact(n-1, res*n);
  }
}