So, I was in HackerRank, trying to learn some pyhton, like any other begginer,
and then I come to the question of "Introduction to Sets"
The task require to do seemed pretty simple to me… at first:
Computer inputs N, wich is a integer and arr, wich is a list, and your job is to write a code that takes the numbers of arr, to be divided by N. Simple right? Not for me, apparently
I would like to know: what the hell does ":" in front of a variable do like in :
if array[:_+1].count(array[_]) == 1:
And why does make the count method work, i searched and found nothing, and I heard this is a good place to ask, sooo, any ideias?
I tried sum all numbers in a online calculator, but it would only give me the result i would get with my own code.
After some try and error of coding i came up to this:
if len(array) != n: print (array) del array[len(array)] print (array) arr = sum(array) print (arr) array = arr / n print (array) return ('%.3f') %array else: print (array) array = sum(array) print (array) print (array) return ('%.3f') %(array/n)
(Yeah, i know its bad)
But apparently, that wasnt enough because, it was always giving me a wrong answer, so i decided to find something in the discussion tab, and I found this:
def average(array): sum_ = 0; count = 0 for _ in range(len(array)): if array[:_+1].count(array[_]) == 1: sum_ += array[_] count += 1 return '%.3f' % (sum_/count,)
I try it and, surprise surprise, it worked !!!
Like… in the first try
And the the difference its like… OUTSTANDING!!
0.775, a difference of 0.775
my code give me 168.600; this other code gives 169.375
if that’s relevant, i use Visual Studio Code
I also changed ‘_’ to ‘a’ to see if changes anytthing, and no
n = 10 arr = [161, 182, 161 ,154 ,176, 170, 167, 171, 170 ,174] result = average(arr) print(result)
srry for bad engrish
array[2:4] gives you the elements 2 and 3 from the array. Generally,
array[start:end] will give you a slice of the array beginning with index
start and stopping one before index
end (that means, slice ranges are left-inclusive and right-exclusive).
Now, there’s a few shortcuts. If you leave out
start, the slice will just start at the beginning of the array:
array[:end] is the same as
array[0:end]. If you leave out the
end, the slice will just run to the end of the array.
array[:_+1] will give you a slice of the array starting at index 0 and running up to index
_+1 exclusive, i.e. up to index