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Damian Brdej
Damian Brdej

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Selection sort algorithm

Let's look at the "top" tab on, there is a list with the most popular articles on the portal. To display it, first we need to sort all articles by number of views. To do that we can use Selection sort algorithm.

The principle of this algorithm is very simple - we search the list of articles looking for the one with the highest number of views, then we copy it to the first index in the newly created list and remove this item from the old list. We repeat these steps until we have a sorted list.

def findBiggest(arr):
    biggest = arr[0]
    biggest_index = 0

    for i in range(1, len(arr)):
        if arr[i] > biggest:
            biggest = arr[i]
            biggest_index = i
    return biggest_index

def selectionSort(arr):
    newArr = []

    for i in range(len(arr)):
        biggest = findBiggest(arr)
    return newArr

print(selectionSort([51, 32, 63, 2, 101])) # [101, 63, 51, 32, 2]
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The algorithm although simple is very slow with a large amount of data, so the developers surely used something faster. The speed of this algorithm specified in Big O notation is O(n2), since we have to search every element in the list.

More about Big O notation you can read in my previous post here

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