Find longest sequence of zeros in binary representation of an integer.
https://app.codility.com/programmers/lessons/1-iterations/binary_gap/
Check whether array A is a permutation.
https://app.codility.com/programmers/lessons/4-counting_elements/perm_check/
Find the smallest positive integer that does not occur in a given sequence.
https://app.codility.com/programmers/lessons/4-counting_elements/missing_integer/
Find the missing element in a given permutation.
https://app.codility.com/programmers/lessons/3-time_complexity/perm_missing_elem/
Compute number of distinct values in an array. https://app.codility.com/programmers/lessons/6-sorting/distinct/