// Marty Stepp, CSE 142, Spring 2010
// This program demonstrates a method to reverse an array.
// Its purpose is to demonstrate array parameters and reference semantics.

import java.util.*;   // for Arrays class

public class Reverse {
    public static void main(String[] args) {
        //       index    0   1   2   3   4   5
        int[] numbers = {11, 42, -5, 27,  0, 89};

        // desired contents after call:
        //              {89, 0,  27, -5, 42, 11}
        // swap 0 - 5
        // swap 1 - 4
        // swap 2 - 3
        // ...

        reverse(numbers);
        System.out.println("The array is " + Arrays.toString(numbers));
        reverse(numbers);
        System.out.println("The array is " + Arrays.toString(numbers));
        
        // demonstrate making a copy so the original won't be damaged
        int[] numbers2 = Arrays.copyOf(numbers, numbers.length);
        Arrays.sort(numbers2);
        System.out.println("The array 2 is " + Arrays.toString(numbers2));
        System.out.println("The array 1 is " + Arrays.toString(numbers));
    }
    
    // Rearranges the elements of the given array into reverse order.
    // Example: [10, 20, 30, 40] -> [40, 30, 20, 10]
    public static void reverse(int[] numbers) {
        for (int i = 0; i < numbers.length / 2; i++) {
            swap(numbers, i, numbers.length - 1 - i);
        }
    }

    // Swaps the elements at the given two indexes.
    // Example: ([10, 20, 30, 40], 0, 2) -> [30, 20, 10, 40]
    public static void swap(int[] a, int index1, int index2) {
        int temp = a[index1];
        a[index1] = a[index2];
        a[index2] = temp;
    }
    
/*
    // longer version that doesn't call swap
    public static void reverse(int[] numbers) {
        for (int i = 0; i < numbers.length / 2; i++) {
            int temp = numbers[i];
            numbers[i] = numbers[numbers.length - 1 - i];
            numbers[numbers.length - 1 - i] = temp;
        }
    }
*/
}