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twice

Language/Type: C++ HashSet Set collections
Author: Marty Stepp (on 2016/06/29)

Write a function named twice that accepts as a parameter a reference to a vector of integers and returns a set containing all the numbers in the vector that appear exactly twice. For example, if a vector variable v stores {1, 3, 1, 4, 3, 7, -2, 0, 7, -2, -2, 1}, the call of twice(v) should return the set {3, 7}.

If you want an extra challenge: Use only Sets as auxiliary storage.

Type your solution here:


This is a function problem. Write a C++ function as described. Do not write a complete program; just the function(s) above.

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