290. One Missing, One Repeated

An array of n values should contain every integer from 1 to n exactly once. In fact one value appears twice and one is missing entirely.

Print the repeated value and then the missing one, separated by a space.

1 2 2 4 -> 2 3

Because the values are guaranteed to lie between 1 and n, a counting array indexed by value works and needs no hashing at all. That is worth noticing: when the keys are small consecutive integers, an array IS the fastest possible hash table.

Constraints - `2 ≤ n ≤ 200000` - `1 ≤ a[i] ≤ n` - Exactly one value repeats and exactly one is missing.