public int factorialSum(int num)

{

LinkedList<Integer> list = new LinkedList<Integer>();

list.add(1);

int retSum = 0;

for ( int i = 2; i <= num; i++ )

list = multiply(list, i);

for ( int i = 0; i < list.size(); i++ )

retSum += list.get(i);

for ( int i = list.size() - 1; i >= 0; i-- )

System.out.print(list.get(i));

System.out.println();

return retSum;

}

public LinkedList<Integer> multiply(LinkedList<Integer> list, int num)

{

LinkedList<Integer> ret = new LinkedList<Integer>(); // sum list

LinkedList<Integer> cur = new LinkedList<Integer>(); // temp list, for current multiplication result

// product is the result of product, carry is for any carry overs, tmp is for last digit of num when mod 10

// count is for number of digits, digit is for getting digit from ret list

int prod = 0, carry = 0, tmp = num, count = 0, digit = 0;

int i = 0;

while ( tmp != 0 )

{

for ( i = 0; i < list.size(); i++ )

{

// basic calculation of product and carry

prod = ( ( list.get(i) ) * ( tmp % 10 ) + carry ) % 10;

carry = ( ( list.get(i) ) * ( tmp % 10 ) + carry ) / 10;

cur.add(prod);

}

// if one loop further, add 0 to front. this is to match length (start) with return list

if ( count != 0 ) cur.push(0);

// this is to add the carry over digit to the end of cur list

if ( carry != 0 ) cur.add(carry);

carry = 0;

for ( i = 0; i < ret.size(); i++ )

{

digit = ret.get(i);

// the reason to use digit is to not mess up with carry, since the digit is updated in place

// so the updated carry will be different

ret.set(i, ( digit + cur.get(i) + carry ) % 10);

carry = ( digit + cur.get(i) + carry ) / 10;

}

// if same length, add to front

if ( i == cur.size() ) if ( carry != 0 ) ret.add(carry);

// not same length, add extra numbers to front

while ( i < cur.size() )

{

ret.add(( cur.get(i) + carry ) % 10);

carry = ( cur.get(i) + carry ) / 10;

i++;

}

count++;

tmp = tmp / 10;

cur.clear();

}

return ret;

}