Selection Sort

H
I
package sort

/**
 * This method implements the Generic Selection Sort
 *
 * @param array The array to be sorted
 * Sorts the array by repeatedly finding the minimum element from unsorted part and putting in the beginning
 *
 * Worst-case performance	O(n^2)
 * Best-case performance	O(n^2)
 * Average performance	O(n^2)
 * Worst-case space complexity	O(1)
 **/
fun <T : Comparable<T>> selectionSort(array: Array<T>) {
    val length = array.size - 1

    for (i in 0..length) {
        var idx = i
        for (j in i + 1..length) {
            if (array[j] < array[idx]) {
                idx = j
            }
        }

        swapElements(array, i, idx)
    }
}
이 알고리즘에 대해

Problem Statement

Given an unsorted array of n elements, write a function to sort the array

Approach

  • select the smallest element from the array
  • put it at the beginning of the array
  • then select the smallest array from the remaining unsorted list
  • append it to the sorted array at the beginning
  • keep doing this for every element of the array
  • repeat the above process n times

Time Complexity

O(n^2) Worst case performance

O(n^2) Best-case performance

O(n^2) Average performance

Space Complexity

O(1) Worst case

Example

arr[] = {80, 10, 40, 30}
Indexes: 0   1   2   3    

1. Index = 0
	Select the minimum number from the array (between index 0-3), ie, 10
2. Swap 10  and 80 (arr[0])
3. The array now is {10, 80, 40, 30}

4. Index = 1
	Select the minimum number from the array (between index 1-3), ie, 30
5. Swap 30 and 80 (arr[1])
6. The array now is {10, 30, 40, 80}

7. Index = 2
	Select the minimum number from the array (between index 2-3), ie, 40
8. Swap 40 and 40 (arr[2])
9. The array now is {10, 30, 40, 80}

The array is now sorted.

Video Explanation

A video explaining the Selection Sort Algorithm

Animation Explanation