This is a
solution to
problem 8 on the
hard interview questions node. If you have not read the
question, the
following will make no
sense to you:
For the first part, compute the sum of the numbers from 1 to N-1. Then sum the values in the array. The duplicate number is the difference between these sums.
For the second part, compute the sum of the numbers from 1 to N+1. Then sum the values in the array. The missing number is again the difference between these sums.