Selection sort idea

Find the minimum each round and place it at the front.

Selection sort logic

Selection sort finds the smallest element in the array and places it at the first position, then repeats for the remaining part.

At each step, the smallest is selected from the unsorted part and placed at the end of the sorted part. This builds the sorted array from the start.

Finding the minimum

To find the smallest element, you scan all elements and track the smallest so far. This requires O(n) operations.

Finding the minimum is the building block of selection sort. At each step, a minimum is found and placed in the right position.

Exercise Find minimum index

Write find_min_index(arr). Return the index of the smallest element. Print 3 with print(find_min_index([5, 2, 8, 1, 9])).

Show example solution

def find_min_index(arr):
    # Find minimum index
    min_idx = 0
    for i in range(1, len(arr)):
        if arr[i] < arr[min_idx]:
            min_idx = i
    return min_idx
print(find_min_index([5, 2, 8, 1, 9]))

Test yourself

What does selection sort do at each step?
- Computes hash
- Swaps neighbors
- Splits array in half
- Finds smallest and places it
Show answer

Finds smallest and places it — Finds smallest and places it.

Minimum index

The smallest element's index is kept in ____.

Show answer

The smallest element's index is kept in min_idx.

Selection sort idea: match the terms

Selection sort

Pick smallest
Minimum

O(n) search
Swap

Exchange
O(n^2)

Complexity

Next lesson: Finding the minimum

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