package Sort

object SelectionSort {

  /** @param array
    *   - a sequence of unsorted integers
    * @return
    *   - sequence of sorted integers @array
    */
  def selectionSort(array: Array[Int]): Array[Int] = {

    for (i <- 0 to array.length - 1) {

      var min: Int = i
      var minVal   = array(i)

      for (j <- i + 1 to array.length - 1) {
        if (array(j) < minVal) {
          min = j
          minVal = array(j)
        }
      }

      val temp: Int = array(i)
      array(i) = array(min)
      array(min) = temp

    }

    array
  }
}

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

• Tute Board