Solutions to exciting final practice problems

Problem A

	// Indexing is much easier going from back to front
	public static void deleteSevens(ArrayList<Integer> alist) {
		for (int i = alist.size()-1; i >= 0; i--) {
			if (alist.get(i) % 7 == 0 || contains7v2(alist.get(i))) {
				alist.remove(i);
			}
		}
	}

	// One way of writing contains7 is to use Strings and concatenation...
	public static boolean contains7(int n) {
		return ("" + n).contains("7");
	}

	// Another way is to use integer division and modular arithmetic
	public static boolean contains7v2(int n) {
		while (n > 0) {
			if (n % 10 == 7) {
				return true;
			} else {
				n /= 10;
			}
		}

		return false;
	}
	
	public static void main(String[] args) {
		ArrayList<Integer> alist = new ArrayList<Integer>();
		for (int i = 0; i < 100; i++) {
			alist.add(i+1);
		}
		deleteSevens(alist);
		System.out.println(alist);
	}

Problem B

	public static String[] prepend(String[] strings, String prefix) {
		String[] strs = new String[strings.length];

		for (int i = 0; i < strs.length; i++) {
			strs[i] = prefix + strings[i];
		}

		return strs;
	}
	

Problem C

public class Rectangle {
	private double left;
	private double top;
	private double width;
	private double height;

	public Rectangle(double left, double top, double width, double height) {
		this.left = left;
		this.top = top;
		this.width = width;
		this.height = height;
	}

	public double getLeft() { return left; }
	public double getTop() { return top; }
	public double getWidth() { return width; }
	public double getHeight() { return height; }

	public double area() { return width * height; }
	public double perimeter() { return 2 * width + 2 * height; }
	public double diagonal() {
		return Math.sqrt(width * width + height * height);
	}

	public String toString() {
		return "{ " + getLeft() + ", " + getTop() + ", " +
	                  getWidth() + ", " + getHeight() + " }";
	}

}