text: Subtract LinkedList Helper is a recursive function , move till the last Node , and subtract the digits and create the Node and return the Node . If d1 < d2 , we borrow the number from previous digit .
code: def subtractLinkedListHelper ( l1 , l2 ) : NEW_LINE INDENT global borrow NEW_LINE if ( l1 == None and l2 == None and not borrow ) : NEW_LINE INDENT return None NEW_LINE DEDENT l3 = None NEW_LINE l4 = None NEW_LINE if ( l1 != None ) : NEW_LINE INDENT l3 = l1 . next NEW_LINE DEDENT if ( l2 != None ) : NEW_LINE INDENT l4 = l2 . next NEW_LINE DEDENT previous = subtractLinkedListHelper ( l3 , l4 ) NEW_LINE d1 = l1 . data NEW_LINE d2 = l2 . data NEW_LINE sub = 0 NEW_LINE DEDENT