CODEWITHSUNDEEP
pythonalgorithmsortingquicksort
Denis K
Denis K

Reputation: 49

Quicksort Python sorting trouble

def quicksort(mas):
    if mas:
        mid = mas[0]
        menshe = [i for i in mas[1:] if i < mid]
        bolshe = [i for i in mas[1:] if i >= mid]
        return quicksort(menshe) + [mid] + quicksort(bolshe)
    else: 
        return mas

n = int(input())
mas = input().split()
print(*quicksort(mas))

It fails on some tests, for example 

input:
3
8 21 22
output:
21 22 8

how to improve the code?

Upvotes: 3

Views: 163

Answers (2)

DAle
DAle

Reputation: 9117

Your quicksort implementation seems to be correct, but you forgot to convert your input to integers. You are sorting strings.

As a side note: don't forget that pivot selection strategy is very important in quicksort algorithm. Your "first element as a pivot" scheme is similar to Lomuto partition scheme that easily degrades to O(n^2) for ordered or almost ordered sequences.

Upvotes: 3

quamrana
quamrana

Reputation: 39354

Your code may very well work. I've yet to test it. (but now that I have it seems correct)

Your mistake is that you discard your first input. So, you should use your own code like this:

mas = input().split()
print(*quicksort(mas))

You only need one input.

Also, you are sorting strings, not necessarily numbers, so you may want to do this:

mas = input().split()
print(*quicksort([int(item) for item in mas]))

Upvotes: 1

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