Project Euler＃3获得数字的最大素因子 [英] Project Euler #3 Get largest prime factor of a number

问题描述

因此，问题如下：

13195的主要因素是5,7,13和29.
最大数字的质数因子600851475143？

我为问题编写了一个代码，其逻辑和算法似乎正确，但似乎找不到错误，有代码。

I made a code for the question whose logic and algorithm seems correct but I can't seem to find the mistake, there's the code.

#include <iostream>

using namespace std;

int main()
{
    long int x = 600851475143;
    for(long int i=x-1; x%i; --i);
    cout << i;
    return 0;
}

RE：不知道'i'我学校的教师没有告诉我=）[不责备他们]

RE: Didn't know about the 'i' scope, Teachers in my school didn't tell me =) [not blaming them]

：Thanx为你的所有回复，我得到的答案。 =）

推荐答案

有两个小问题和一个大问题：

There are two small issues and one big issue:

• 您的 i 变量超出了打印范围 - 语句的头部以语句本身结束。在这种情况下， i 在分号后不可见，因此您需要在之外声明


• 您的变量不一定包含您想要放入的值 - long 32位类型，在许多平台上，它是。要使其至少为64位类型，请将声明更改为 long long 。

• Your i variable is out of scope for printing - the scope of variables declared in the header of the statement ends with the statement itself. In this case, i is not visible after the semicolon, so you need to declare it outside the for
• Your variables may not necessarily hold the values that you want to put into them - long is allowed to be a 32-bit type, and on many platforms, it is. To make it at least a 64-bit type, change the declaration to long long.

一旦你修复这些问题，你的代码将编译。但是，由于代码的第三个，大的问题，它需要花费很长时间才能运行：您的算法太慢了。

Once you fix these problems, your code will compile. However, it will take ages to run because of the third, big, problem with your code: your algorithm is too slow.

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