I haven't taken a C++ class in over a year and I am asking for some help. I do not want anyone to give me the answer just to walk me through how to answer this.

Here is the question:

Design an algorithm for finding the closest 2 numbers in the input list

so let say I have 5 numbers: 8, 5, 12, 20, and 1. How would I start this? It is supposed to be an unsorted list. I have an idea of how I would do it if the list was sorted, but since its not I do not know where to start. Any help would be greatly appreciated!