G - Gathering Red-Black Fruits
Time limit: 3 seconds
Memory limit: 256 megabytes
Languages: MS C# .NET 4.7.2053,GNU G++11 5.1.0
It's harvest time at Farmer Fred's orchard of red-black trees! But since he's too old to climb trees, Fred brought all his grandchildren to the orchard for a competition of fruit gathering: those who collect the most fruits will be awarded red-black jam jars!
Red-black trees are special, because the same tree gives two different kinds of fruit: the red fruit and the black fruit. That gives Farmer Fred a problem: how to rank children who collected the same amounts of different fruits? For instance, if Abby picked two red and three black fruits, and Bruce picked three red and two black fruits, who should rank higher in the competition? How much should each fruit be worth?
To solve this problem, Farmer Fred decided that each red fruit would be worth $r$ points, and each black fruit would be worth $b$ points, both $r$ and $b$ positive integers. Then he would rank the kids according to the total number of points each one has, ties broken arbitrarily.
All that's left to do now is choose the values of $r$ and $b$. But Farmer Fred got curious, and now he wants to know in how many different ways he can rank his grandchildren according to the described criteria. Two rankings are considered different if, and only if, there is any child who has different positions in them.