Solution to 16.9

src/TechInterview/ArithmeticOperations.java

@@ -0,0 +1,221 @@
+package TechInterview;
+
+public class ArithmeticOperations {
+
+	/**
+	 * Used for subtract and divide
+	 * @param a 	the value to find the inverse of
+	 * @return int	the additive inverse of the given value
+	 */
+	private static int inverse(int a) {
+		//The inverse of 0 is 0
+		if(a == 0) {
+			return a;
+		}
+
+		int temp = a;
+		int posOrNeg;
+		int result = 0;
+
+		//If a is positive, then the value of the additive inverse will be negative
+		if(temp > 0) {
+			posOrNeg = -1;
+		}
+		//If a is negative, then the value of the additive inverse will be positive
+		else {
+			posOrNeg = 1;
+		}
+
+		/*
+		 * temp increments towards zero, starting from a
+		 * result increments in the same direction, starting from zero
+		 * When temp = 0, result = |a|, but with the opposite sign
+		 */
+		while(temp != 0) {
+			result += posOrNeg;
+			temp += posOrNeg;
+		}
+
+		return result;
+	}
+
+	/**
+	 * Subtracts the subtrahend from the minuend
+	 * @param minuend		the number to be subtracted from
+	 * @param subtrahend	the number to subtract
+	 * @return	int			the difference
+	 */
+	public static int subtract(int minuend, int subtrahend) {
+		//Subtraction is essentially adding the additive inverse of the second number
+		int neg = inverse(subtrahend);
+		return minuend + neg;
+	}
+
+	/**
+	 * Divides the first value by the second value
+	 * @param dividend		the value to divide from
+	 * @param divisor		the value to divide by
+	 * @return	int			the quotient
+	 * @throws IllegalArgumentException	
+	 */
+	public static int divide(int dividend, int divisor) throws IllegalArgumentException {
+		int quotient = 0;
+		int value = dividend;
+		int temp = divisor;
+		boolean positiveDividend = true;
+		boolean positiveDivisor = false;
+
+		//Cannot divide by zero
+		if(temp == 0) {
+			throw new IllegalArgumentException("Cannot divide by zero");
+		}
+		//Dividing zero by any number will equal zero
+		else if(value == 0) {
+			return 0;
+		}
+		//If the dividend is negative, set it positive and make positiveDividend false
+		if(value < 0) {
+			value = inverse(value);
+			positiveDividend = false;
+		}
+		//If the divisor is positive, set it negative and make positiveDivisor true 
+		if(temp > 0) {
+			temp = inverse(temp);
+			positiveDivisor = true;
+		}
+
+		/*
+		 * In each iteration of the loop, value is reduced by |divisor|
+		 * Also, quotient is incremented
+		 * When value <= 0, quotient will be the number of times that 
+		 * |divisor| can be subtracted from value 
+		 */
+		while(value + temp >= 0) {
+			quotient++;
+			value += temp;
+		}
+
+		/*
+		 * If both of the signs of the dividend and the divisor are the same, 
+		 * the quotient is positive
+		 */ 
+		if(positiveDividend == positiveDivisor) {
+			if(quotient < 0) {
+				quotient = inverse(quotient);
+			}
+		}
+		/*
+		 * If both of the signs of the dividend and the divisor are different, 
+		 * the quotient is negative
+		 */
+		else {
+			if(quotient > 0) {
+				quotient = inverse(quotient);
+			}
+		}
+		return quotient;
+	}
+
+	/**
+	 * Multiplies the multiplicand by the multiplier
+	 * @param multiplier		the number to multiply
+	 * @param multiplicand		the number that gets multiplied
+	 * @return	int 			the product
+	 */
+	public static int multiply(int multiplicand, int multiplier) {
+		int product = 0;
+		int value = multiplicand;
+
+		//If the multiplicand is negative, set it to be positive
+		if(value < 0) {
+			value = inverse(value);
+		}
+
+		//Multiplication can be seen as repetitive addition
+		for(int i = 0; i < value; i++) {
+			product += multiplier;
+		}
+
+		/*
+		 * If the signs of the multiplicand and the multiplier are the same,
+		 * then the product should be positive
+		 */
+		if(multiplicand < 0 && multiplier < 0) {
+			product = inverse(product);
+		}
+		/*
+		 * If the signs of the multiplicand and the multiplier are different,
+		 * then the product should be negative
+		 */
+		else if(multiplicand < 0 && multiplier > 0) {
+			product = inverse(product);
+		}
+		return product;
+	}
+
+	/**
+	 * Used for testing that each of the functions works.
+	 * @param args
+	 */
+	public static void main(String[] args) {
+		//Testing multiply
+		System.out.print("0 * 4 = ");
+		System.out.println(multiply(0, 4));
+		System.out.print("4 * 0 = ");
+		System.out.println(multiply(4, 0));
+		System.out.print("0 * 0 = ");
+		System.out.println(multiply(0, 0));
+		System.out.print("2 * 5 = ");
+
+		System.out.println(multiply(2, 5));
+		System.out.print("7 * -9 = ");
+
+		System.out.println(multiply(7, -9));
+		System.out.print("-7 * 9 = ");
+		System.out.println(multiply(-7, 9));
+		System.out.print("-7 * -9 = ");
+		System.out.println(multiply(-7, -9));
+
+		//Testing divide
+		System.out.print("0 / 2 = ");
+		System.out.println(divide(0, 2));
+		try {
+			System.out.print("7 / 0 = ");
+			System.out.println(divide(7, 0));
+		}
+		catch(IllegalArgumentException e) {
+			System.out.println("Invalid input.");
+		}
+
+		System.out.print("4 / 3 = ");
+		System.out.println(divide(4, 3));
+
+		System.out.print("10 / -5 = ");
+		System.out.println(divide(10, -5));
+		System.out.print("-10 / 5 = ");
+		System.out.println(divide(-10, 5));
+		System.out.print("-10 / -5 = ");
+		System.out.println(divide(-10, -5));
+
+		//Testing subtract
+		System.out.print("7 - 0 = ");
+		System.out.println(subtract(7, 0));
+		System.out.print("0 - 7 = ");
+		System.out.println(subtract(0, 7));
+		System.out.print("0 - 0 = ");
+		System.out.println(subtract(0, 0));
+
+		System.out.print("4 - 3 = ");
+		System.out.println(subtract(4, 3));
+		System.out.print("2 - 5 = ");
+		System.out.println(subtract(2, 5));
+
+		System.out.print("6 - -5 = ");
+		System.out.println(subtract(6, -5));
+		System.out.print("-6 - 5 = ");
+		System.out.println(subtract(-6, 5));
+		System.out.print("-6 - -5 = ");
+		System.out.println(subtract(-6, -5));
+
+	}
+}

src/TechInterview/SinglyLinkedList.java

@@ -44,7 +44,7 @@ public Node remove(int index) {
     }
 
     public E get(int index) {
-        if (index > 0 && index < size) {
+        if (index >= 0 && index < size) {
             Node curr = head;
             for (int i = 0; i <= index; i++) {
                 curr = curr.next;
@@ -81,6 +81,10 @@ public String toString() {
         return sb.toString();
     }
 
+    public int size() {
+    	return size;
+    }
+
     public class Node {
 
         private Node next;