If v1 is a vector containing some number of int elements sorted in ascending order, after these statements execute: std::vector results1; Std::vector results2; Std::unique_copy(v1.begin(), v1.end(), std::back_inserter(results1)); Std::reverse_copy(v1.begin(), v1.end(), std::back_inserter(results2)); Which of the following could be true? A) results1 contains more elements than results2. B) The first element in results1 matches the last element in results2. C) results1 is empty but results2 is not. D) None of the above.

Question

Quizplus · Accepted Answer

The first statement, `std::unique_copy(v1.begin(), v1.end(), std::back_inserter(results1))`, copies the unique elements in `v1` to `results1`. Since `v1` is sorted in ascending order, `results1` will also contain a sorted list of unique elements.
The second statement, `std::reverse_copy(v1.begin(), v1.end(), std::back_inserter(results2))`, copies the elements in `v1` in reverse order to `results2`. Since `v1` is sorted in ascending order, `results2` will contain a reverse sorted (i.e. sorted in descending order) list of elements.
Therefore, the first element in `results1` (since it contains unique, sorted elements) will match the last element in `results2` (since it contains a reverse sorted list of elements).

If V1 Is a Vector<int> Containing Some Number of Int