Finding the first n largest elements in an array

Question

I have got an array containing unique elements. I need to find out the first n largest elements in the array in the least complexity possible. The solution that I could thin

Answer 1

The usual trick to select the n largest elements is to maintain a min-priority queue.

• Unconditionnally insert into the queue the n first elements
• For each remaining element x, insert x if it is greater than the least element of the queue (O(log n) operation), and remove the least element (O(log n)).
• When done, the priority queue contains n elements, which are the n largest elements of the original array.

Total complexity: O(N log n) where N is the total number of elements in the array.

I leave to you as an exercise the implementation details (first step is to learn about priority queues, and implement one).