private void validateInput(int[] numbers) {
    if (numbers == null) {
      throw new IllegalArgumentException("You can't pass a null instance of numbers.");
    }
    if (numbers.length == 0) {
      throw new IllegalArgumentException("You can't pass an empty array");
    }
  }
Iterative algorithm to solve this problem. This solution is based on the summation definition,
if the array has every element from 0 to N except one, then we can calculate the sum of every
element in the summation and the real sum to subtract both values and find the missing number.
The complexity order in time terms is O(N) where N is the number o elements in the array. In
space terms, the complexity order is O(1) because we are not using any auxiliary data
structure with a size related to the input data to resolve this problem.
src/main/java/com/github/pedrovgs/problem72/FindTheMissingNumber.java