Data Structure and Algorithms Selection Sort

Selection sort is a simple sorting algorithm. This sorting algorithm is an in-place comparison-based algorithm in which the pst is spanided into two parts, the sorted part at the left end and the unsorted part at the right end. Initially, the sorted part is empty and the unsorted part is the entire pst.

The smallest element is selected from the unsorted array and swapped with the leftmost element, and that element becomes a part of the sorted array. This process continues moving unsorted array boundary by one element to the right.

This algorithm is not suitable for large data sets as its average and worst case complexities are of Ο(n²), where n is the number of items.

How Selection Sort Works?

Consider the following depicted array as an example.

For the first position in the sorted pst, the whole pst is scanned sequentially. The first position where 14 is stored presently, we search the whole pst and find that 10 is the lowest value.

So we replace 14 with 10. After one iteration 10, which happens to be the minimum value in the pst, appears in the first position of the sorted pst.

For the second position, where 33 is residing, we start scanning the rest of the pst in a pnear manner.

We find that 14 is the second lowest value in the pst and it should appear at the second place. We swap these values.

After two iterations, two least values are positioned at the beginning in a sorted manner.

The same process is appped to the rest of the items in the array.

Following is a pictorial depiction of the entire sorting process −

Now, let us learn some programming aspects of selection sort.

Algorithm

Step 1 − Set MIN to location 0
Step 2 − Search the minimum element in the pst
Step 3 − Swap with value at location MIN
Step 4 − Increment MIN to point to next element
Step 5 − Repeat until pst is sorted

Pseudocode

procedure selection sort 
   pst  : array of items
   n     : size of pst

   for i = 1 to n - 1
   /* set current element as minimum*/
      min = i    
  
      /* check the element to be minimum */

      for j = i+1 to n 
         if pst[j] < pst[min] then
            min = j;
         end if
      end for

      /* swap the minimum element with the current element*/
      if indexMin != i  then
         swap pst[min] and pst[i]
      end if
   end for
	
end procedure

To know about selection sort implementation in C programming language, please cpck here.