Selection sort is an algorithm that sorts a list of elements by repeatedly finding the minimum element from the unsorted part of the list and swapping it with the element in the current position. It does this by iterating through the list from beginning to end, selecting the minimum element at each iteration and swapping it into place. The time complexity of selection sort is O(n^2) in both the average and worst cases, making it inefficient for large lists.

1. SORTING ALGORITHMS
SELECTION SORT

6. Selection Sort
(Cards Example)

7. Initial Configuration
(search all cards and find the largest)

8. Swap the two cards

9. As before, the swap is
performed in three steps.

10. Sorted Unsorted
Among the remaining cards
the king is the largest.
It will remain in place.
But the algorithm may perform
Some empty operations
(ie., swap it with itself in place)

11. Sorted Unsorted
Among the remaining cards
the queen is the largest.
It will remain in place.
But the algorithm may perform
Some empty operations
(i.e., swap it with itself in place)

12. Sorted Unsorted
Among the remaining cards
the Jack is the largest.
It will remain in place.
But the algorithm may perform
Some empty operations
(i.e., swap it with itself in place)

13. As before, the swap is
performed in three steps.

14. Sorted Unsorted
We are down to the last card.
Because there is only one and
Because we know that it is
Smaller than all the rest
We don’t need to do anything
Else with it. This is why the
Algorithm goes up to < N-1

15. Sorted
All cards are now sorted.

16. Selection Sort
[http://web.ics.purdue.edu/~cs154/lectures/lecture010.htm]

17. Example:
Selection
Sort
[http://web.ics.purdue.edu/~cs154/lectures/lecture010.htm]

18. Example: Selection Sort.c

19. // Selection Sort
#include <stdlib.h>
#define N 6
int main()
{
int a[N]= { 23, 78, 45, 8, 32, 56};
int i,j;
// Sort the array using Selection Sort
int minIndex;
for(i=0; i < N-1; i++)
{
// find the minimum element in the unsorted part of the
array
minIndex=i;
for(j=i+1; j < N; j++)
if(a[j] < a[minIndex])
minIndex = j;
// Swap a[i] with the smallest element
int temp = a[i];
a[i] = a[minIndex];
a[minIndex] = temp;
}
system("pause");

20. Time Complexity
• Analysis of the worst case:
– Outer loop executes N-1 times (no exch rqd. for final element).
– Inner loop executes N-i-1 comparisons.
(N-1) + (N-2) + … + 2 + 1 = N*(N-1)/2 = O(N2
)
The worst case occurs if the array is already sorted in descending order.
 Best Case = O (n^2)
 Average Case = O(n^2)
Selection sort is an inplace sorting algorithm. So its takes
constant O(1) space.

21. Advantages
– Easy to write
– Can be done “in place”
– Can be done on linked lists too (keep a tail pointer)

22. Disadvantages
– It is about N2
even in the best case for
comparisons.
– So the running time (over all inputs) is
approximately O(N2
).
– The primary disadvantage of selection sort is its
poor efficiency when dealing with a huge list of
items.