Knowledge Base > Algorithms & Data Structures > Sorting Algorithms

Selection Sort

Algorithm Analysis

The selection sort works by selecting the smallest unsorted item remaining in the list, and then swapping it with the item in the next position to be filled. The selection sort has a complexity of O(n2).

Pros: Simple and easy to implement.
Cons: Inefficient for large lists, so similar to the more efficient insertion sort that the insertion sort should be used in its place.

Empirical Analysis

Selection Sort Efficiency
Selection Sort Efficiency Graph

The selection sort is the unwanted stepchild of the n2 sorts. It yields a 60% performance improvement over the bubble sort, but the insertion sort is over twice as fast as the bubble sort and is just as easy to implement as the selection sort. In short, there really isn't any reason to use the selection sort - use the insertion sort instead.

If you really want to use the selection sort for some reason, try to avoid sorting lists of more than a 1000 items with it or repetitively sorting lists of more than a couple hundred items.

Source Code
Below is the basic selection sort algorithm.

void selectionSort(int numbers[], int array_size)
  int i, j;
  int min, temp;

  for (i = 0; i < array_size-1; i++)
    min = i;
    for (j = i+1; j < array_size; j++)
      if (numbers[j] < numbers[min])
        min = j;
    temp = numbers[i];
    numbers[i] = numbers[min];
    numbers[min] = temp;

A sample C program that demonstrates the use of the selection sort may be downloaded here.

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