## Editorial for DMPG '19 B6 - Oddity

Remember to use this editorial

**only**when stuck, and**not to copy-paste code from it**. Please be respectful to the problem author and editorialist.**Submitting an official solution before solving the problem yourself is a bannable offence.**Author:

Let be the number of stamp types that friend has and let be the number of stamp types that Alice has. Observe that Alice satisfies the constraints if and only if is odd for all . So the only important feature of a collection for this problem is the parity of the number of stamp types. Then Alice should either take the cheapest stamp type, or the cheapest two stamp types, or it is impossible. Checking which of these possibilities works can be easily done by checking the parity of each .

**Time Complexity:**

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