/**
* Utility method to split the list into two
*
* @param left : Starting index for split
* @param right : Ending index for the split
* @return : Returns an object of the BigArithmetic class with the list split
*/
public G05_BigArithmetic split(int left, int right) {
G05_BigArithmetic temp = new G05_BigArithmetic();
for (int i = left; i < right; i++) {
temp.number.add(this.number.get(i));
}
temp.effectiveSize = temp.number.size();
return temp;
}
/**
* DAC Algorithm to multiply two long numbers
*
* @param a : Input object of BigArithmetic class
* @param b : Input object of BigArithmetic class
* @return : Returns an object of the BigArithmetic class which is a product of the two inputs
*/
public static G05_BigArithmetic product(G05_BigArithmetic a, G05_BigArithmetic b) {
// If any of the two lists is null return null
if (a == null || b == null) {
return null;
}
// We remove the MS zeros to get the effective size of the two numbers.
G05_BigArithmetic x = a.removeMSZeros();
G05_BigArithmetic y = b.removeMSZeros();
/*If the size is zero, then the list is 0, so return zero - Multiply by zero */
if (x.effectiveSize == 0 || y.effectiveSize == 0) {
return new G05_BigArithmetic(0L);
}
// Call the productBA for DAC
G05_BigArithmetic c = productBA(x, y);
return c;
}
/**
* Method to multiply the two Big Arithmetic objects
*
* @param a : Input - object of class BigArithmetic
* @param b : Input - object of class BigArithmetic
* @return : Returns the product of the two inputs.
*/
public static G05_BigArithmetic productBA(G05_BigArithmetic a, G05_BigArithmetic b) {
int maxSize = Math.max(a.effectiveSize, b.effectiveSize); // Get the max size of the two lists
// If max size is one - normal single digit multiplication
if (maxSize <= 1) {
return new G05_BigArithmetic(a.number.get(0) * b.number.get(0));
}
// If any of the lists is small - pad zeros to make the size equal
if (a.number.size() < maxSize) {
a.addZero(maxSize - a.number.size());
} else if (b.number.size() < maxSize) {
b.addZero(maxSize - b.number.size());
}
// Get the middle of the two lists
int mid = (maxSize + 1) / 2;
// Find a1, a2, b1 and b2
G05_BigArithmetic a1 = a.split(0, mid);
G05_BigArithmetic a2 = a.split(mid, maxSize);
G05_BigArithmetic b1 = b.split(0, mid);
G05_BigArithmetic b2 = b.split(mid, maxSize);
G05_BigArithmetic temp1 = productBA(a1, b1); // a1*b1
G05_BigArithmetic temp2 = productBA(a2, b2); // a2*b2
G05_BigArithmetic temp12 =
productBA(G05_BigArithmetic.add(a1, a2), G05_BigArithmetic.add(b1, b2)); // (a1+a2)*(b1+b2)
// [(a1+a2)*(b1+b2) - {(a1*b1) + (a2*b2)}]
G05_BigArithmetic temp =
G05_BigArithmetic.subtract(temp12, G05_BigArithmetic.add(temp1, temp2));
temp12 = temp;
// Pad zeroes - similar to raising to base
temp12 = temp12.addLeastZero(mid);
temp2 = temp2.addLeastZero(mid * 2);
// Return the product while removing MS Zeros
return G05_BigArithmetic.add(G05_BigArithmetic.add(temp2, temp12), temp1).removeMSZeros();
}
/**
* Method to subtract two large numbers
*
* @param a : Input a - an object of the BigArithmetic Class.
* @param b : Input b - Second object of the BigArithmetic Class.
* @return : An object of the type BigArithmetic, that contains the result of the subtraction.
*/
public static G05_BigArithmetic subtract(G05_BigArithmetic a, G05_BigArithmetic b) {
boolean sign = false, bo = false; // Two boolean flags to represent sign and borrow
/*
* If second number is bigger than first, swap the two and set sign to true
* We will return zero if sign is still set to true - Level 1 - No negative nos.
*/
if (a.number.size() < b.number.size()) {
G05_BigArithmetic t = b;
b = a;
a = t;
sign = true;
}
/*
* If the size of the two numbers are equal, then iterate to see if second is bigger than first.
* If yes, swap and set sign as true like the previous case.
* Else, we are good to continue with the subtraction, so break out of the loop.
*/
else if (a.number.size() == b.number.size()) {
for (int i = a.number.size() - 1; i >= 0; i--) {
if (a.number.get(i) < b.number.get(i)) {
sign = true;
G05_BigArithmetic t = b;
b = a;
a = t;
continue;
} else break;
}
}
// Iterators for looping through the linked list.
Iterator<Long> ita = a.number.iterator();
Iterator<Long> itb = b.number.iterator();
G05_BigArithmetic result = new G05_BigArithmetic();
Long diff, firstElement = nextElement(ita), secondElement = nextElement(itb);
while (secondElement != null) {
if (bo) {
if (firstElement == 0) {
firstElement = 9L;
bo = true;
} else {
firstElement = firstElement - 1;
bo = false;
}
}
if (firstElement < secondElement) {
firstElement += 10;
bo = true;
}
diff = firstElement - secondElement;
result.number.add(diff % B);
firstElement = nextElement(ita);
secondElement = nextElement(itb);
}
while (firstElement != null) {
if (bo) {
if (firstElement == 0) {
firstElement = 9L;
bo = true;
} else {
firstElement = firstElement - 1;
bo = false;
}
}
result.number.add(firstElement);
firstElement = nextElement(ita);
}
// If sign, result is a negative number - so return zero
if (sign) {
return new G05_BigArithmetic(0L);
}
// Remove the most significant zeros from the list.
result.removeMSZeros();
// If after removing the zeros the size is zero, we return the answer as zero
if (result.effectiveSize == 0) {
return new G05_BigArithmetic(0L);
}
return result;
}