Unique Pattern

I'll show you the standard pattern for removing all duplicates from a container. First, sort the elements: sort(v.begin(), v.end()) to group duplicates together. Then call unique and erase together: v.erase(unique(v.begin(), v.end()), v.end()).

This shrinks the vector to contain only the distinct elements in sorted order. The final vector is sorted with no duplicates remaining. Total time complexity is $O(n \log n)$ dominated by the sorting step.

This pattern appears in many problems.