private int negate(int number) {
    int increment = number > 0 ? -1 : 1;
    int result = 0;
    while (number != 0) {
      result += increment;
      number += increment;
    }
    return result;
  }
Iterative algorithm to resolve this problem. This solution is based on the subtraction
definition where the subtraction is defined as the sum of the second number negated.
src/main/java/com/github/pedrovgs/problem73/SubtractAdding.java