Selection Sort

Selection sort is an algorithm for sorting a list of items. It works by repeatedly selecting the smallest remaining item and moving it to the front of the list. Here's a simple implementation of selection sort in Python:

def selection_sort(items):
  for i in range(len(items) - 1):
    # Find the minimum element in the unsorted portion of the list
    min_index = i
    for j in range(i+1, len(items)):
      if items[j] < items[min_index]:
        min_index = j

    # Swap the minimum element with the first element of the unsorted portion
    items[i], items[min_index] = items[min_index], items[i]
  return items 

To sort a list of items using selection sort, you would call the selection_sort function and pass in the list of items as an argument. For example:

sorted_items = selection_sort([5, 2, 8, 1, 9])
print(sorted_items)  # prints [1, 2, 5, 8, 9]

Selection sort has a time complexity of O(n^2), which means that it is not a very efficient algorithm for large lists. It is more suitable for small lists or lists that are almost sorted.

Is selection sort a divide and conquer algorithm?

No, selection sort is not a divide and conquer algorithm.

Divide and conquer algorithms work by dividing a problem into smaller subproblems, solving each subproblem individually, and then combining the solutions to the subproblems to solve the original problem. Selection sort, on the other hand, works by repeatedly selecting the smallest remaining item in the list and moving it to the front of the list. It does not divide the problem into smaller subproblems.

Selection sort belongs to the category of sorting algorithms known as comparison-based sorting algorithms, which work by comparing elements in the list and rearranging them based on their relative values. Other examples of comparison-based sorting algorithms include bubble sort and insertion sort.

Selection sort has a time complexity of O(n^2) meaning?
The time complexity of an algorithm is a measure of how long the algorithm takes to run, as a function of the size of the input. In the case of selection sort, the time complexity is O(n^2), which means that the running time of the algorithm is proportional to the square of the size of the input.

More specifically, the time complexity of selection sort is O(n^2) because the inner loop (the loop over j) runs n times for each iteration of the outer loop (the loop over i), and there are n iterations of the outer loop. This means that the total number of iterations of the inner loop is n * n = n^2, which is why the time complexity of selection sort is O(n^2).

This means that selection sort is not a very efficient algorithm for large lists, as the running time increases quickly with the size of the input. For example, if the input size is doubled (from n to 2n), the running time will increase by a factor of 4 (from n^2 to 4n^2).