arrays - Python: find the largest prime number of X -


hey awesome python people,

warning: new coding. ok, have been warned...

i trying write python file finds largest prime number of variable declare inside code.

here thought process:

step 1:find factors of x step 2:put factors of x in array step 3:analyze last element of array step 4:check if last element of array prime step 5: if last element of array prime print "found largest prime" along number itself, else, analyze second last element in array a, , on until @ a[1] step 6: if no prime numbers in array, print "no primes found"

the issue somewhere in last else statement, when dealing x=28 , factors in array: [1, 2, 4, 7, 14] code thinks 7 not prime...

my steps listed in-line:

#find factors, put them in array  #1.find factors of x #2.put factors of x in array  x=28 i=1 a=[] length = 0  while i<x:           if x%i == 0:    #checks see if x divisible between 1 , x-1         a.append(i)  #adds factor array     = i+1           print "your factors are: ", "\n", print "\n"   #3. analyze last element in array # before loop below, = [1, 2, 4, 7, 14] , length = 5  length = 0 length = len(a) n=a[length-1]-1   print "checking primes in 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 prime"  #added         del a[-1]         length = len(a)          print "length = ",length         if length == 2:             print "no primes"

a few questions:

  • how re-assign variables x, a[], , n make code more readable

  • in second loop, after first iteration, when analyzing 7 why code not recognize prime number?

thanks constructive feedback!!

ok, this: 

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))

first use primes function took here. returns array containing prime factors. then, aply max-function, gives largest element of array.

the output follows: 

factors:  [2, 2, 7] largest is:  7

i hope helps.


Comments

Post a Comment

Popular posts from this blog

javascript - RequestAnimationFrame not working when exiting fullscreen switching space on Safari -

request animation frame stops working when exiting fullscreen clicking on original space's safari window. fine if fullscreen mode canceled escape key or calling cancelfullscreen(). steps reproduce: open https://dl.dropboxusercontent.com/u/769042/prezi/safari-fullscreen.html click "draw raf", kittie appears click "fullscreen", go fullscreen click "draw raf", kittie appears go space original safari was, showing "click exit fullscreen mode", click anywhere, out fullscreen click "draw raf", nothing happens what handling click calling: window.requestanimationframe(draw); which draws on canvas context: function draw() { ctx.drawimage(img, math.random()*500|0, math.random()*400|0, 100, 100); } i checked .hidden , .visibilitystate, updated correctly. tested on osx 10.9.3, safari 7.0.4 (9537.76.4). has workaround/solution other switching old settimeout? this sounds webkit bug 88940 : using reque...
Read more

jsf - How to ajax update an item in the footer of a PrimeFaces dataTable? -

this visual of table have: +---------+------------+-------------------+ | header1 | header2 | header3 | +---------+------------+-------------------+ | row | input | calc'ed output | | row b | input b | calc'ed output b | | etc.. | etc.. | etc.. | +---------+------------+-------------------+ | total: total calc'ed output | +------------------------------------------+ and stripped-down code: <p:datatable id="mytable" value="#{mybean.somelist}" var="currentitem"> <p:column headertext="header1"> <h:outputtext value="#{currentitem.name}" /> </p:column> <p:column headertext="header2"> <pe:inputnumber value="#{currentitem.inputval}"> <p:ajax event="change" listener="#{mybean.changelistener}" update="outputval outputtotal...
Read more

django - CSRF verification failed. Request aborted. CSRF cookie not set -

error: reason given failure: csrf cookie not set. in general, can occur when there genuine cross site request forgery, or when django's csrf mechanism has not been used correctly. post forms, need ensure: browser accepting cookies. view function uses requestcontext template, instead of context. in template, there {% csrf_token %} template tag inside each post form targets internal url. if not using csrfviewmiddleware, must use csrf_protect on views use csrf_token template tag, accept post data. you're seeing section of page because have debug = true in django settings file. change false, , initial error message displayed. can customize page using csrf_failure_view setting. did find, nothing helped, must foolish(( my template <form method="post">{% csrf_token %} {% field in form %} <div class="control-group"> {{ field }} </div> {% endfor %} <input type=...
Read more