SelectionSort.java

// Author: Alara Dasdan
// Date: Jul 2020

package Sorting;

import java.util.Random;

// Sorting numbers using the selection sort algorithm
public class SelectionSort {
	static int seed = 12345; // random number generator seed
	static int sz = 10; // size of the array

	// generate rand num in a given range
	public static double randDouble(Random rd, double min, double max) {
		return min + rd.nextDouble() * (max - min + 1);
	}
	
	// generate array of random numbers
	public static double[] getRandNumbers(int sz) {
		Random rd = new Random(seed);
		double[] arr = new double[sz];  // array of random numbers

		// generate random numbers
		for (int i = 0; i < arr.length; i++) {
			double r = randDouble(rd, 0, 10);
			arr[i] = r;
		}

		return arr;
	}
	
	// print input array arr in given order; also verify if sorted
	public static void printNums(double[] arr, boolean isAscending) {
		System.out.format("\nprint array of size %d:\n", arr.length);
		String sep = "";
		for (int i = 0; i < arr.length; i++) {
			System.out.format(sep + "%.2f", arr[i]);
			sep = ", ";
		}
		System.out.println();
		boolean isSorted = checkSort(arr, isAscending);
		System.out.println("is sorted? " + isSorted);	
	}

	// swap arr[x] and arr[y]
	private static void swap(double[] arr, int x, int y) {
		double tmp = arr[x];
		arr[x] = arr[y];
		arr[y] = tmp;
	}
	
	// sort input array in place
	public static void sortInPlace(double[] arr, boolean isAscending) {
		for (int i = 0; i < arr.length; i++) {
			double min = arr[i];
			double max = arr[i];
			int kMin = i;
			int kMax = i;
			for (int j = i; j < arr.length; j++) {
				if (arr[j] <= min) {
					min = arr[j];
					kMin = j;
				}
				if (arr[j] >= max) {
					max = arr[j];
					kMax = j;
				}

			}
			// swap arr[i] and arr[j] to move new min to beginning
			if (isAscending) {
				swap(arr, i, kMin);
			} else {
				swap(arr, i, kMax);
			}
		}
	}
	
	// sort input array into a new array and return it
	public static double[] sort(double[] arr, boolean isAscending) {
		double[] arr2 = arr;
		sortInPlace(arr2, isAscending);
		return arr2;
	}

	// verify if arr is sorted in the given order
	public static boolean checkSort(double[] arr, boolean isAscending) {
		for (int j = 0; j < (arr.length - 1); j++) {
			if (isAscending) {
				if (arr[j] > arr[j + 1]) {
					return false;
				}
			} else {
				if (arr[j] < arr[j + 1]) {
					return false;
				}
			}
		}
		return true;
	}
	
	public static void main(String[] args) {
		boolean isAscending = true;
		double[] arr = getRandNumbers(sz); 
		printNums(arr, isAscending);
		
		double[] arr2 = sort(arr, isAscending);
		printNums(arr2, isAscending);
		
		arr = getRandNumbers(0);
		printNums(arr, isAscending);
		
		arr2 = sort(arr, isAscending);
		printNums(arr2, isAscending);

		arr = getRandNumbers(1);
		printNums(arr, isAscending);
		
		arr2 = sort(arr, isAscending);
		printNums(arr2, isAscending);

	}
}