Finding the minimum
- Algorithms course
- Beginner
- Lesson 26/80
- 4 min
Find the index of the minimum in a slice.
Swapping
Once the minimum is found, you swap it with the first element of the unsorted part. This places that element in its correct position.
Swapping takes O(1) time: only two elements are exchanged. In total, n-1 swaps are performed.
Sorted part growth
After each swap, the sorted part grows by one element. Selection sort expands the sorted part from the start to the end.
At step i, the first i elements are sorted and the rest are unsorted. At the last step, the whole array is sorted.
Practice Swap elements
Write swap_min(arr, i, min_idx). Swap arr[i] and arr[min_idx], return arr. Print [1, 3, 2] with print(swap_min([3, 1, 2], 0, 1)).
Starter code
def swap_min(arr, i, min_idx):
# Swap two elementsSample solution
def swap_min(arr, i, min_idx):
# Swap two elements
arr[i], arr[min_idx] = arr[min_idx], arr[i]
return arr
print(swap_min([3, 1, 2], 0, 1))Expected output
[1, 3, 2]
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Swap
Swap two elements: arr[i], arr[min_idx] = ____Swap two elements: arr[i], arr[min_idx] = arr[min_idx]Explanation: arr[min_idx] is right.
2 Finding the minimum: match the terms
| Term | Meaning |
|---|---|
Swap |
Exchange |
min_idx |
Minimum index |
O(1) |
Swap time |
n-1 |
Swap count |
3 How long does a swap take?
- O(log n) Correct answer
- O(n^2)
- O(n)
- O(1)
Explanation: A swap is O(1).