Instruction

Code for Selection Sort

Python

# This code here at the top is the same as we saw in the Bogosort
# example. It just loads a Python list of numbers from a file.
import sys
from load import load_numbers

numbers = load_numbers(sys.argv[1])

# Let's implement the function that will do our selection sort.
# We're going to pass in our Python list containing all the unsorted
# numbers.
def selection_sort(values):
  # We'll create an empty list that will hold all our sorted values.
  sorted_list = []
  # We'll loop once for each value in the list.
  for i in range(0, len(values)):
    # We call a function named index_of_min, which we're going to
    # write in just a minute, that find the minimum value in the
    # unsorted list and return its index.
    index_to_move = index_of_min(values)
    # Then we call the "pop" method on the list, and pass it the
    # index of the minimum value. pop will remove that item from the
    # list and return it. We then add that value at the end of the
    # sorted list.
    sorted_list.append(values.pop(index_to_move))
  # Going up a level of indentation signals to Python that we're
  # ending the loop. After the loop finishes, we return the sorted
  # list.
  return sorted_list

# Now we need to write the function that picks out the minimum value.
# We pass in the list we're going to search.
def index_of_min(values):
  # We mark the first value in the list as the minimum. It may or may
  # not be the actual minimum, but it's the smallest we've seen on
  # this pass through the list. (It's also the only value we've seen
  # on this pass through the list so far.)
  min_index = 0
  # Now we loop through the remaining values in the list after the
  # first.
  for i in range(1, len(values)):
    # We test whether the value we're currently looking at is less
    # than the previously recorded minimum.
    if values[i] < values[min_index]:
      # If it is, then we set the current index as the new index of
      # the minimum value.
      min_index = i
  # After we've looped through all the values, we return the index of
  # the smallest value we found.
  return min_index

# Lastly, we need to actually run our selection sort method, and
# print the sorted list it returns.
print(selection_sort(numbers))

Let's try running it! Save the above code in a file named selection_sort.py, in the same directory as bogosort.py and load.py (see the instructions for Bogosort if you don't have those files). You can run it on the numbers in the 5.txt file with this terminal command:

python selection_sort.py numbers/5.txt

JavaScript

function indexOfMin(list) {
    var minIndex = 0;
    for(var i = 0; i < list.length; i++) {
        if (list[i] < list[minIndex]) {
            minIndex = i;
        }
    }
    return minIndex;
}

function selectionSort(list) {
    var sortedList = [];
    while(list.length > 0) {
        var indexToMove = indexOfMin(list);
        sortedList.push(list.splice(indexToMove, 1)[0]);
    }
    return sortedList;
}

const testValues = [29, 100, 1, 2, 57, 28, 88, 3, 50, 67, 37, 1, 32, 20];

var sorted = selectionSort(testValues);
console.log(sorted);

Java

import java.util.*;

public class Sort {
    static ArrayList<Integer> selectionSort(ArrayList<Integer> list) {
        ArrayList<Integer> sortedList = new ArrayList<Integer>();
        int length = list.size();
        for(int i = 0; i < length; i++) {
            int indexToMove = indexOfMin(list);
            int min = list.get(indexToMove);
            list.remove(indexToMove);
            sortedList.add(min);
        }
        return sortedList;
    }

    static int indexOfMin(ArrayList<Integer> list) {
        int minIndex = 0;
        int length = list.size();
        for (int i = 0; i < length; i++) {
            if(list.get(i) < list.get(minIndex)) {
                minIndex = i;
            }
        }
        return minIndex;
    }

    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<Integer>(Arrays.asList(29, 100, 1, 2, 57));
        System.out.println(selectionSort(list));
    }
}

C-Sharp

using System;
using System.Collections.Generic;

namespace SelectionSort
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            var list = new List<int>() { 29, 100, 1, 2, 57 };
            var sortedList = SelectionSort(list);
            Console.WriteLine(String.Join(",", sortedList));
        }

        static List<int> SelectionSort(IList<int> list)
        {
            var sortedList = new List<int>();
            while (list.Count > 0)
            {
                int indexToMove = IndexOfMin(list);
                int min = list[indexToMove];
                list.RemoveAt(indexToMove);
                sortedList.Add(min);
            }
            return sortedList;
        }

        static int IndexOfMin(IList<int> list)
        {
            int minIndex = 0;
            for (int i = 0; i < list.Count; i++)
            {
                if (list[i] < list[minIndex])
                {
                    minIndex = i;
                }
            }
            return minIndex;
        }
    }
}

Algorithms: Sorting and Searching

Code for Selection Sort

Python

JavaScript

Java

C-Sharp