Division of very big numbers in O(n) where n is the number of digits of the big number.

gistfile1.cpp

int D[3000];
int len;
 
int Mod(int x) {
  int res = 0;
  for (int i = len-1; i >= 0; --i)
    res = (res * 10 + D[i]) % x;    
  return res;
}
 
void Div(int x) {
  int left = 0, will;
  for (int i = len-1; i >= 0; --i) {
    will = (left * 10 + D[i]) % x;    
    D[i] = (left * 10 + D[i]) / x;    
    left = will;
  }
  while (len && D[len-1] == 0) len--;
}