Write methods to implement the multiply, subtract and divide operations for integers. Use only the add operator.

CC150-7.4.java

package POJ;

import java.util.ArrayList;

public class Main{
 
	/**
	 * 
	 * 7.4	Write methods to implement the multiply, subtract and divide operations for integers. Use only the add operator.
	 * 
	 */
	public static void main(String[] args) {
		Main so = new Main();
		int subtraction = so.divide(-99, -40);
		System.out.println("subtraction=" + subtraction);
	}

	public int subtraction(int a, int b) {
		return a + negate(b);
	}

	private int negate(int a) {
		// TODO Auto-generated method stub
		int neg = 0;
		int b = (a < 0) ? 1 : -1;
		while (a != 0) {
			a += b;
			neg += b;
		}
		return neg;
	}

	public int multiply(int a, int b) {
		if (a < b) {
			// algorithm is faster if b<a
			return multiply(b, a);
		}
		int sum = 0;
		for (int i = abs(b); i > 0; i--) {
			sum += a;
		}
		if (b < 0)
			sum = negate(sum);
		return sum;
	}

	private int abs(int b) {
		// TODO Auto-generated method stub
		if (b < 0)
			return negate(b);
		else
			return b;
	}

	public int divide(int a, int b) {
		if (b == 0)
			throw new java.lang.ArithmeticException();
		int absa = abs(a);
		int absb = abs(b);
		int product = 0;
		int x = 0;
		while (absb + product <= absa) {
			product += absb;
			x++;
		}
		if ((a > 0 && b > 0) || (a < 0 && b < 0))
			return x;
		else
			return negate(x);
	}
}