Humongous Factorial Digit Sum!

The Pascal code

function GetDigitSum(num: Integer): Integer;
var
bn:array[0..200000] of Integer;
st,en,car,a,b,temp,base: Integer;

begin
  base := 1000;
  for a := 0 to 200000 do bn[a] := 0;
  bn[0] := 1;
  st := 0;
  en := 0;
  for a := 2 to num do
    begin
      car := 0;
      for b := st to en do
      begin
        temp := a*bn[b] + car;
        bn[b] := temp mod base;
        car := temp div base;
      end;
      while car > 0 do
        begin
          Inc(en);
          bn[en] := car mod base;
          car := car div base;
        end;
      while bn[st] = 0 do Inc(st);
    end;
  Result := 0;
  for a := st to en do
    begin
      b := bn[a];
      while b > 0 do
        begin
          Result := Result + (b mod 10);
          b := b div 10;
        end;
    end; 
end;

does the trick (doing the calculations in base $1000$ , and fixing matters to use optimal integer datatypes). It calculates the value of $149346$ for the digit sum of $10000!$ in $0.78$ s, and obtains the answer $\boxed{1938780}$ for the digit sum of $100000!$ in $1$ minute $54$ seconds.

Solution in Java:

import java.math.BigInteger;

public class FactorialSum {

public static void main(String[] args) {
    int p=1;
    BigInteger m=new BigInteger("1");

    while(p<=100000) {
        BigInteger n= BigInteger.valueOf(p);

m=m.multiply(n);
p++;}
    String j=new String(m.toString());
    int f=j.length();
    int s=0;
    int sum=0;
    while(s<f) {
        int d=j.charAt(s)-'0';
        sum+=d;
        s++;
    }
    System.out.println(sum);


}

}