素数数组 [英] Array of prime numbers

问题描述

我刚开始让我的手脏的红宝石，想知道是否有人能帮助我这个阵列质数的例子。我有问题了项目欧拉，我想红宝石打印素数的数组。但是，每次我运行程序时，其输出仅仅是0。有人可以在这里提供一些线索。谢谢你在前进。

  DEF黄金
    X = 13195
    数= 0
    一个= []
    而计数＆LT; X
        如果count％×== 0
            a.push（计数）
            a.sort
        结束
        数+ = 1
    结束
    把一个
结束
 

解决方案

假设你想测试，如果 13195 是一个素数，并且希望一个来保持一个列表，其中数分为 13195

您需要启动计数 2时，因为包括黄金每一个数字是整除1.您还需要使用 x％的计数，而不是计数％X 。 x％的计数由数除以x和给你剩下的（这是正确的检查，对0）。

  DEF黄金
    X = 13195
    数= 2
    一个= []
    而计数＆LT; X
        如果x％计数== 0
            a.push（计数）
        结束
        数+ = 1
    结束
    一个
结束ARR =总理
p ARR＃此会打印出它融入13195号列表
arr.size == 0 #true如果数字是一个素数，否则为false
 

请注意，有很多的优化可以在这个算法做检查，如果一个数是素数 - 也就是你的循环条件可以是：

 开方=的Math.sqrt（X）
而计数＆LT;开方
 

您只需要检查到你数的平方根，看它是否是一个素数

I just started getting my hands dirty on ruby and was wondering if someone can help me with this array of primes example. I got the problem off of project Euler, and I want ruby to print an array of prime numbers. However, every time I run the program, it outputs just "0". Can someone shed some light here. Thank you in advance.

def prime
    x = 13195
    count = 0
    a = [ ]
    while count < x
        if count % x == 0
            a.push(count)
            a.sort
        end
        count += 1
    end
    puts a
end

解决方案

Assuming you want to test if 13195 is a prime, and you want a to keep a list of which numbers divide into 13195

You need to start count at 2, since every number including a prime is divisible by 1. You also need to use x % count instead of count % x. x % count divides x by count and gives you the remainder (which are correctly checking against 0 for).

def prime
    x = 13195
    count = 2
    a = [ ]
    while count < x
        if x % count == 0
            a.push(count)
        end
        count += 1
    end
    a
end

arr = prime 
p arr #this will print out a list of numbers which fit into 13195
arr.size == 0 #true if number is a prime, false otherwise

Note that there is a lot of optimizations you can do in this algorithm to check if a number is a prime - namely your for loop condition can be:

sqrt = Math.sqrt(x)
while count < sqrt

you only need to check up to the square root of your number to see if it's a prime

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