Select Sort

Selection Sort

The Selection Sort is a very basic sort. It works by finding the smallest element in the array and putting it at the beginning of the list and then repeating that process on the unsorted remainder of the data. Rather than making successive swaps with adjacent elements like bubble sort, selection sort makes only one, swapping the smallest number with the number occupying its correct position.

Consider the following unsorted data: 8 9 3 5 6 4 2 1 7 0. On the first iteration of the sort, the minimum data point is found by searching through all the data; in this case, the minimum value is 0. That value is then put into its correct place at the beginning of the list by exchanging the places of the two values. The 0 is swapped into the 8's position and the 8 is placed where the 0 was, without distinguishing whether that is the correct place for it, which it is not.

Now that the first element is sorted, it never has to be considered again. So, although the current state of the data set is 0 9 3 5 6 4 2 1 7 8, the 0 is no longer considered, and the selection sort repeats itself on the remainder of the unsorted data: 9 3 5 6 4 2 1 7 8.

Consider a trace of the insertion sort algorithm on a ten element data set:

8 9 3 5 6 4 2 1 7 0
0 9 3 5 6 4 2 1 7 8
0 1 3 5 6 4 2 9 7 8
0 1 2 5 6 4 3 9 7 8
0 1 2 3 6 4 5 9 7 8
0 1 2 3 4 6 5 9 7 8
0 1 2 3 4 5 6 9 7 8
0 1 2 3 4 5 6 9 7 8
0 1 2 3 4 5 6 7 9 8
0 1 2 3 4 5 6 7 8 9