freeCodeCamp Algorithm Selection Sort Guide

freeCodeCamp Algorithm Selection Sort Guide
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The selection sort algorithm sorts an array by repeatedly finding the minimum element (considering ascending order) from the unsorted part and putting it at the beginning. The algorithm maintains two subarrays in a given array.

  1. The subarray which is already sorted.
  2. Remaining subarray which is unsorted.

In every iteration of selection sort, the minimum element (considering ascending order) from the unsorted subarray is picked and moved to the sorted subarray.

Example

Animation of SelectionSort

arr[] = 64 25 12 22 11

# Placing the minimum element in arr[0...4] in the beginning
11 25 12 22 64

# Placing the minimum element in arr[1...4] in the beginning
11 12 25 22 64

# Placing the minimum element in arr[2...4] in the beginning
11 12 22 25 64

# Placing the minimum element in arr[3...4] in the beginning
11 12 22 25 64

C++ Implementation

void selection_sort(int array[], int n)
{
    // Contains index of minimum element in unsorted subarray
    int min_index;

    // Move boundary of unsorted subarray
    for(int i = 0; i < n-1; i++)
    {
        // Find the minimum element in unsorted subarray
        min_index = i;
        for(int j = i+1; j < n; j++)
        {
            // If present element is less than element at min_index
            // Then change min_index to present index
            if(array[j] < array[min_index])
            {
                min_index = j;
            }
        }

        // Swap the element at min_index with the first element
        int temp;
        temp = array[min_index];
        array[min_index] = array[i];
        array[i] = temp;
    }
}

:rocket: Run Code

Python Implementation

def selection_sort(arr):
    for i in range(len(arr)):
        min_x = i
        for j in range(i+1,len(arr)):
            if arr[j] < arr[min_x]:
                min_x = j
        arr[min_x], arr[i] = arr[i], arr[min_x]

arr = [64, 25, 12, 22, 11]
selection_sort(arr)
print(arr) # Prints [11, 12, 22, 25, 64]

:rocket: Run Code

Complexity of Algorithm

Time Complexity: O(n*n) Due to the two nested loops.


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