You can also use partial_sort method if you don't mind about ordering.
http://www.cplusplus.com/reference/algorithm/partial_sort/[
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Although for 2 item, it might be overkill, if you want say the 10 biggest items, it might be a good idea to use standard (STL) algorithms.
Otherwise solution 1 is appropriate and you might modify it slightly if for example, you want to properly handle the case when all values are the minimal possible value as that algorithm would return index 0 twice in such case.