private void borrow(int[] a, int initialPosition) {
int borrowPosition = initialPosition + 1;
if (a[borrowPosition] == 0) borrow(a, borrowPosition);
a[initialPosition] += 10;
--a[borrowPosition];
}
private int[] subtract(int[] a, int[] b) {
int biggerSize = a.length;
int smallerSize = b.length;
int[] result = new int[biggerSize];
for (int i = 0; i < smallerSize; ++i) {
if (a[i] < b[i]) borrow(a, i);
result[i] = a[i] - b[i];
}
int sizeDifference = biggerSize - smallerSize;
if (sizeDifference > 0) System.arraycopy(a, smallerSize, result, smallerSize, sizeDifference);
return result;
}