sort array of integers lexicographically C++

Question

I want to sort a large array of integers (say 1 millon elements) lexicographically.

Example:

input [] = { 100, 21 , 22 , 99 , 1  , 927 }
sorted[] = { 1           


        

Answer 1

A compact solution if all your numbers are nonnegative and they are small enough so that multiplying them by 10 doesn't cause an overflow:

template bool lex_less(T a, T b) {
  unsigned la = 1, lb = 1;
  for (T t = a; t > 9; t /= 10) ++la;
  for (T t = b; t > 9; t /= 10) ++lb;
  const bool ll = la < lb;
  while (la > lb) { b *= 10; ++lb; }
  while (lb > la) { a *= 10; ++la; }
  return a == b ? ll : a < b;
}

Run it like this:

#include 
#include 
int main(int, char **) {
  unsigned short input[] = { 100, 21 , 22 , 99 , 1  , 927 };
  unsigned input_size = sizeof(input) / sizeof(input[0]);
  std::sort(input, input + input_size, lex_less);
  for (unsigned i = 0; i < input_size; ++i) {
    std::cout << ' ' << input[i];
  }
  std::cout << std::endl;
  return 0;
}