[英]Python: find the largest prime number of X
嘿,很棒的python人,
警告:我是編碼新手。 好吧,現在您已經被警告了...
我正在嘗試編寫一個python文件,該文件查找我在代碼內聲明的變量的最大素數。
這是我的思考過程:
Step 1:Find Factors of X
Step 2:Put factors of X in an array a
Step 3:Analyze last element of array a
Step 4:Check if last element of array a is Prime
Step 5: if last element of array a is prime print "found the largest prime" along with the number itself, else, analyze second to last element in array a, and so on until at a[1]
Step 6: if no prime numbers in array, print "no primes found"
問題在最后一個else語句中的某個地方,當處理x = 28及其數組中的因子時:[1、2、4、7、14]我的代碼認為7不是素數...
我的步驟已在線列出:
#find factors, put them in an array a
#1.Find factors of X
#2.Put factors of X in an array a
x=28
i=1
a=[]
length = 0
while i<x:
if x%i == 0: #checks to see if X is divisible by anything between 1 and X-1
a.append(i) #adds factor to array a
i = i+1
print "your factors are: ", "\n", a
print "\n"
#3. Analyze the last element in array a
# Before loop below, a = [1, 2, 4, 7, 14] and length = 5
length = 0
length = len(a)
n=a[length-1]-1
print "checking for primes in your array now...", "\n"
while len(a) > 2:
if a[length-1]%n != 0:
n=n-1
if n == 1:
print "PRIME TIME"
break
else:
print a[length-1], "is not a prime" #added
del a[-1]
length = len(a)
print "length = ",length
if length == 2:
print "NO Primes"
幾個問題:
您將如何重新分配x,ia []和n之類的變量以使代碼更具可讀性
在第二個循環中,在第一次迭代之后,當分析7時,為什么代碼無法識別出它是質數?
非常感謝您的建設性反饋!!
好的,我會這樣做:
def primes(n):
primfac = []
d = 2
while d*d <= n:
while (n % d) == 0:
primfac.append(d)
n /= d
d += 1
if n > 1:
primfac.append(n)
return primfac
print "Factors: ", primes(28)
print "The largest is: ", max(primes(28))
首先使用我從這里獲取的primes
函數。 它返回一個包含所有素數的數組。 然后,簡單地使用max-function
,它為您提供了數組中最大的元素。
輸出如下:
Factors: [2, 2, 7]
The largest is: 7
我希望這有幫助。
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