Selection Sort Algorithm

How does a selection sort algorithm work?

When dealing with a sorting algorithm like a selection sort, there's a thin line between easy and confusing. However, you got on the right bus at the right station. Today we'll go through the steps towards achieving a good and basic selection sort algorithm.

Okay first thing we want to know is that a selection sort algorithm starts with first element assuming it's the smallest.

Always remember to work with index values, it's better that way. Then compares it to all other elements to see if it is.

For example, in the first iteration of the nested loop, the algorithm will take index y value and compare it with smallest value index, and if the current index value(y) is smaller than the smallest index value, then the algorithm will set y index as the smallest value index, and in the case that y is not, the algorithm will continue to the next index. Now the thing about the selection sort is that, when the iteration number of
the first loop increases the iterations of the second loop shortens.

So, for example if the first loop is on the 5th iteration and the length of the list is 9, the nested loop will only iterate in the of range (5+1, 9) which means it only iterates 3 times in the 5th phase.

How to apply that practically

Anyway, with all that explained, we move on to the practical part.

Create the main 'For Loop'

To begin, we'll create a variable storing our unsorted list, next we create a loop based on the length of the unsorted list, within the loop define a minimum index variable to store the smallest value index.

nums = [4,1,5,3,2,9,7]

for x in range(len(nums)):
    min_index = x

Add the nested 'For Loop'

Now within the loop, create another for loop iterating between the current iteration number of the first loop + 1 and the length of the unsorted list.

nums = [4,1,5,3,2,9,7]

for x in range(len(nums)):
    min_index = x
    for y in range(x+1, len(nums)):

Create conditional statements

In this loop we'll set a condition to determine if the current index value is less than the minimum index value. If that is the case, then we'll set the minimum index to the current index.

nums = [4,1,5,3,2,9,7]

for x in range(len(nums)):
    min_index = x
    for y in range(x+1, len(nums)):
        if nums[y] < nums[min_index]:
            min_index = y

After that, at the end of the nested loop, we'll swap the values of the minimum index(min_index) and the index determined by the first loop(x).

nums = [4,1,5,3,2,9,7]

for x in range(len(nums)):
    min_index = x
    for y in range(x+1, len(nums)):
        if nums[y] < nums[min_index]:
            min_index = y

    nums[x], nums[min_index] = nums[min_index], nums[x]