为什么此代码找不到权力? (红宝石) [英] Why Can't This Code Find Powers? (Ruby)

问题描述

App Academy的实践测试表明，他们选择的查找输入是否为2的幂的方法是在循环上继续将其除以2，并检查最终结果是1还是0(在测试了数字1和2之后， 0作为输入)，这很有意义，但是为什么这种方式不起作用?

App Academy's practice test says their chosen way of finding if an input is a power of 2 is to keep dividing it by 2 on a loop and check whether the end result is 1 or 0 (after having tested for the numbers 1 and 0 as inputs), which makes sense, but why won't this way work?

def try
  gets(num)
  counter = 0
  go = 2 ** counter

  if num % go == 0 
    return true
  else
    counter = counter + 1
  end

    return false
end

除非计数器不起作用，否则我无法弄清楚为什么它不起作用.

I can't figure out why this won't work, unless the counter isn't working.

推荐答案

您的代码存在许多问题.

There are a number of problems with your code.

1. 首先，没有循环，并且由于counter = 0，如果您打算在循环中使用该方法，则每次计数器都会重置为零.

1. First of all, there is no loop and your counter will reset to zero each time if you intend to use the method in a loop, because of counter = 0.

counter = 0; go = 2 ** counter基本上表示go = 2 ** 0，即1.因此，num % 1将始终为0

counter = 0; go = 2 ** counter basically means go = 2 ** 0 which is 1. Therefore num % 1 will always be 0

实际上，您需要对数字进行除法并在此过程中进行更改. 12 % 4将返回0，但您不知道12是否为2的幂.

You actually need to divide the number and change it in the process. 12 % 4 will return 0 but you don't know by that if 12 is a power of 2.

IO#gets 返回一个字符串，并使用分隔符作为参数，因此您需要使用num = gets.to_i来实际获取变量num中的数字.您要将num赋予gets作为参数，但这并不能满足您的要求.

IO#gets returns a string and takes a separator as an argument, so you need to use num = gets.to_i to actually get a number in the variable num. You are giving num to gets as an argument, this does not do what you want.

尝试:

# Check if num is a power of 2
#
# @param num [Integer] number to check
# @return [Boolean] true if power of 2, false otherwise
def power_of_2(num)
  while num > 1 # runs as long as num is larger than 1
    return false if (num % 2) == 1 # if number is odd it's not a power of 2
    num /= 2 # divides num by 2 on each run
  end
  true # if num reached 1 without returning false, it's a power of 2
end

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