javascript 中的非常大的数字
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Extremely large numbers in javascript
提问by JEJoll
I'm working on the Project Euler problems (currently question 13).
我正在处理 Project Euler 问题（当前问题 13）。
For this question I have to find the first 10 digits of the sum of 100 numbers all of a size similar to this:
对于这个问题，我必须找到大小与此类似的 100 个数字之和的前 10 位数字：
91,942,213,363,574,161,572,522,430,563,301,811,072,406,154,908,250
I think I could use something like Java's BigInteger, but I started solving the problems in JavaScript (I'm trying to boost my js abilities for work), and I would like to continue using it, even to solve this problem.
我想我可以使用 Java 的 BigInteger 之类的东西，但是我开始用 JavaScript 解决问题（我正在努力提高我的 js 工作能力），我想继续使用它，甚至解决这个问题。
I'd like to stick to pure JS if possible.
如果可能的话，我想坚持使用纯 JS。
回答by bhspencer
You are going to need a javascript based BigInteger library. There are many to choose from. Here is one https://github.com/peterolson/BigInteger.js
您将需要一个基于 javascript 的 BigInteger 库。有很多可供选择。这是一个https://github.com/peterolson/BigInteger.js
You can use it like this
你可以像这样使用它
var n = bigInt("91942213363574161572522430563301811072406154908250")
.plus("91942213363574161572522430563301811072406154908250");
回答by Qi Fan
Javascript recently got a new primitive data type BigInt(stage 4 proposal as of January 2020).
https://github.com/tc39/proposal-bigint
Javascript 最近获得了一种新的原始数据类型BigInt（截至 2020 年 1 月的第 4 阶段提案）。
https://github.com/tc39/proposal-bigint
Chrome, Firefox and few other browsers have started supporting this in newer versions (check compatibility here), while other browsers are still implementing it.
Chrome、Firefox 和少数其他浏览器已开始在较新版本中支持此功能（在此处检查兼容性），而其他浏览器仍在实现它。
https://developers.google.com/web/updates/2018/05/bigint
https://developers.google.com/web/updates/2018/05/bigint
Basically it can be declared using either literals like
基本上它可以使用任何文字来声明，例如
var a = 1n;
var a = 1n;
or
或者
var b = BigInt('22222222222222222222222222222222');
var b = BigInt('22222222222222222222222222222222');
Math operators don't do auto conversion between BigInt and Number, so
数学运算符不会在 BigInt 和 Number 之间进行自动转换，因此
1 + 1n
will throw an error.
会抛出错误。
回答by Alex McMillan
You could always convert your sum to a string, rip out the .and grab the result - something like this:
你总是可以将你的总和转换为 a string，撕掉.并获取结果 - 像这样：
var sum = 2384762348723648237462348;
sum = sum.toString(); // "2.3847623487236483e+24"
// Rip out the "."
sum = sum.substr(0, 1) + sum.substr(2);
// Grab the first 10 characters
var firstTen = sum.substr(0, 10);
回答by JEJoll
Surprisingly, sticking all the values in an array and adding them all together and just taking the first 10 digits worked. I must have had a typo somewhere in my code when it didn't work before.
令人惊讶的是，将所有值粘贴在一个数组中并将它们加在一起，然后只取前 10 位数字就可以了。当我的代码之前不起作用时，我一定在某处输入了拼写错误。
I'm sure that doing something this simple wouldn't work in all cases (like those @AlexMcmillan and @zerkms have been debating about). I think the safest bet is the BigInteger library mentioned by @bhspencer, but it seems like adding the first x significant digits with y digits as a buffer might also be worth a shot in some cases.
我敢肯定，做这么简单的事情不会在所有情况下都有效（就像@AlexMcmillan 和 @zerkms 一直在争论的那样）。我认为最安全的选择是@bhspencer 提到的 BigInteger 库，但似乎在某些情况下，将前 x 位有效数字与 y 位数字添加为缓冲区也可能值得一试。
回答by cheesehead
I did this using an array and updating all entries with a function.
我使用一个数组并用一个函数更新所有条目。
function f(a) {
for (let i = 0; i < a.length - 1; i++) {
a[i + 1] = a[i + 1] + parseInt(a[i] / 10);
a[i] = a[i] % 10;
}
return a;
}
// remember to init the array with enough elements for all digits
var a = Array(200);
a.fill(0);
a[0] = 1;
Hereis a JSFiddle with the code for problem 20.
这是一个带有问题 20 代码的 JSFiddle。
