Codility Coding Screen

What they ask

For developer roles in Cairo the process is a phone call with HR, a Codility test, then an on-site technical interview. The Codility set is a handful of medium problems in a fixed time; you pick the language.

Questions in this area, for example: given an array of integers a, return the smallest positive integer that does not appear in it.

Examples

• [1, 3, 6, 4, 1, 2] returns 5.
• [1, 2, 3] returns 4.
• [-1, -3] returns 1.

Constraints

• 1 <= a.length <= 10^5, values in [-10^6, 10^6].
• The platform scores both correctness and performance, so an O(n^2) answer passes the visible tests and then fails the hidden ones.

What they look for

• An O(n) time solution (a set, or marking indices in place) rather than sorting and scanning.
• Careful edge cases: negatives, duplicates, an array that is exactly 1..n.
• Clean code you can explain on site. The technical interview that follows usually opens with "walk me through what you submitted".