Find top N elements in an Array

Question

What would be the best solution to find top N (say 10) elements in an unordered list (of say 100).

The solution which came in my head was to 1. sort it using quick s

Answer 1

Yes, you can do it in O(n) by just keeping a (sorted) running list of the top N. You can sort the running list using the regular library functions or a sorting network. E.g. a simple demo using 3, and showing which elements in the running list change each iteration.

5 2 8 7 9

i = 0
top[0] <= 5

i = 1
top[1] <= 2

i = 2
top[2] <= top[1] (2)
top[1] <= top[0] (5)
top[0] <= 8

i = 3
top[2] <= top[1] (5)
top[1] <= 7

i = 4
top[2] <= top[1] (7)
top[1] <= top[0] (8)
top[0] <= 9