24 Containers library [containers]

24.6 Container adaptors [container.adaptors]

24.6.11 Class template flat_set [flat.set] Constructors [flat.set.cons]

explicit flat_set(container_type cont, const key_compare& comp = key_compare());
Effects: Initializes c with std​::​move(cont) and compare with comp, sorts the range [begin(), end()) with respect to compare, and finally erases all but the first element from each group of consecutive equivalent elements.
Complexity: Linear in N if cont is already sorted with respect to compare and otherwise , where N is the value of cont.size() before this call.