import java.util.Arrays;


public class ArrayPractice {
	public static void main(String[] args) {
		int[] a = {10, 20, 30, 40};
		System.out.println("Before: " + Arrays.toString(a));
		swap1st2nd(a);
		System.out.println("After: " + Arrays.toString(a));
		a = new int[]{10, 20, 5, 30, 40};
		System.out.println("Before: " + Arrays.toString(a));
		swap1st2nd(a);
		System.out.println("After: " + Arrays.toString(a));
		a = new int[0]; // empty array
		System.out.println("Before: " + Arrays.toString(a));
		swap1st2nd(a);
		System.out.println("After: " + Arrays.toString(a));
	}
	
	/*
	 * Write a method that takes an array of integers
	 * and that swaps the first and second halves of the array
	 * if the array is [1, 3, 10, 20]
	 * the method would change it to
	 * [10, 20, 1, 3]
	 * and if the array is [1, 3, 5, 10, 20]
	 * the method would change it to
	 * [10, 20, 5, 1, 3]
	 * 
	 * you can't use another array or an array list in 
	 * your solution
	 */
	public static void swap1st2nd(int[] a) {
		// loop over the first half
		for (int i = 0; i < a.length/2; i ++) {
			// corresponding index in the second half
			int j = i + (a.length + 1) / 2;
			// swap a[i] and a[j]
			int temp = a[i];
			a[i] = a[j];
			a[j] = temp;
		}
	}
	

}