用Javascript编写组合和置换计算器的最有效方法 [英] Most efficient way to write Combination and Permutation calculator in Javascript

问题描述

我有一个数学网站 http://finitehelp.com ，该网站教授学生有限数学.我认为包括一个计算器会很酷，所以我用Java编写了一个用于组合和排列的计算器.实时计算器位于 http://finitehelp.com/finite-calculator.html .我对Javascript几乎一无所知，并且会冒险猜测有一种更高效的方法来编写以下代码，尤其是因为过度使用了变量.如果有人可以帮助我，我将非常感激.

I have a math website http://finitehelp.com that teaches students Finite Math. I thought it would be cool to include a calculator so I made one for combinations and permutations in Javascript. Live calculator is at http://finitehelp.com/finite-calculator.html. I know next to nothing about Javascript and would venture to guess there is a much more efficient way to write the following particularly because of the excessive use of variables. If someone could please help me I would be very grateful.

<script type="text/javascript">
// calculate n!
Math.factorial = function(n)
{
    if(typeof n == 'string') n = Number(n);
    if(typeof n != 'number' || isNaN(n))
    {
        alert("Factorial requires a numeric argument.");
        return null;
    }
    if (n < 2) return 1;
    return (n * Math.factorial(n-1));
}
Math.divide = function(a,b)
{
    return a/b;
}
</script>

<form class="form" name="combination" action="">
    <p>C(<input type="text" value="n" name="T1" size="1">,<input type="text" value="r" name="T2" size="1">)
    <input type="button" value="Calculate"
     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;">
    = <input type="text" name="T3" size="12" readonly></p>
</form>

推荐答案

好，我们开始！

首先，为什么还要编写这个?

First of all, why would you ever need to write this?

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

我会完全消除它.

您还可以稍微整理一下 Math.factorial :

You can also clean up your Math.factorial a little bit:

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));
    }
}

但是主要问题是您的 onclick()代码:

But the main problem is your onclick() code:

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;

这太复杂了.我会使其成为一个函数并将其绑定到元素，这将消除HTML中的所有废话，并使其更易于使用:

This is way too complicated. I'd make it a function and bind it to the element, which would get rid of all of the crap in your HTML and make it a bit easier to work with:

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));
    }
}

然后删除 onclick = 代码.

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