- Written by
Ajay Pathak
- Posted November 20, 2012 at 8:35 pm

Selection sort is a sorting algorithm, specifically an in-place comparison sort. It has O(n2) time complexity, making it inefficient on large lists, and generally performs worse than the similar insertion sort. Selection sort is noted for its simplicity, and it has performance advantages over more complicated algorithms in certain situations, particularly where auxiliary memory is limited.

The algorithm divides the input list into two parts: the sublist of items already sorted, which is built up from left to right at the front (left) of the list, and the sublist of items remaining to be sorted that occupy the rest of the list. Initially, the sorted sublist is empty and the unsorted sublist is the entire input list. The algorithm proceeds by finding the smallest (or largest, depending on sorting order) element in the unsorted sublist, exchanging it with the leftmost unsorted element (putting it in sorted order), and moving the sublist boundaries one element to the right

Source : http://en.wikipedia.org/wiki/Selection_sort

Code

public static int[] SelectionSort(int[] input)
{
StreamWriter sw = new StreamWriter(@"Sorting.txt", true);
sw.WriteLine("\n\t\t Selecton Sorting \n");
sw.WriteLine(System.DateTime.Now + "\t input Array \t Total Element \t"

+ input.Length);
sw.WriteLine(string.Join(",", input));
int i, j;
i = j = 0;
int temp = 0;
int iMin = 0;
for (i = 0; i < input.Length; i++)
{
for (j = i + 1; j < input.Length; j++)
{
if (input[j] < input[iMin])
{
iMin = j;
}
}
if (iMin != i && iMin < input.Length)
{
temp = input[iMin];
input[iMin] = input[i];
input[i] = temp;
}
}
sw.WriteLine(System.DateTime.Now + "\t Sorted Array \n"

+ string.Join(",", input));
sw.Close();
return input;
}

Test Case

private static void SelectionSortTest() {
List<int> input = new List<int>();
Random rnd = new Random(1);
int maxnumber = 1200;
input.Clear();
for (int i = 1; i <= maxnumber; i++)
{
input.Add(rnd.Next(1, maxnumber));
}
Sorting.SelectionSort(input.ToArray());
input.Clear();
maxnumber = 100000;
for (int i = 1; i <= maxnumber; i++)
{
input.Add(rnd.Next(1, maxnumber));
}
Sorting.SelectionSort(input.ToArray());
input.Clear();
maxnumber = 10000;
for (int i = 1; i <= maxnumber; i++)
{
input.Add(rnd.Next(1, maxnumber));
}
Sorting.SelectionSort(input.ToArray());
}