Problem H
Cat Coat Colors
Black is usually written as B, Red as O, Dilution as D. In general, a cat has two copies of each gene, one from each parent (except for the red gene which is sex-bound, we’ll return to that later). Each copy can be either dominant, which we’ll denote using an upper case letter, or recessive, which we’ll denote using a lower case letter. Thus for each gene there are three possibilities: either both copies of the gene are dominant, both are recessive, or one is dominant and the other is recessive. When describing a cat we’ll write this as a pair of letters, with the second one possibly being a “-” to indicate a wildcard. For example, “bb” indicates that the cat has two recessive black genes, and “B-” indicates that the cat has a dominant black gene and that we don’t care about whether the other one is dominant or recessive.
When a cat has no dominant red (O) gene, its coat will be a variation of black, according to the following four combinations:
B-D-: Black |
B-dd: Blue |
bbD-: Chocolate |
bbdd: Lilac |
Now, red (O or o) is sex bound on the X chromosone. This means a male cat, or tom, only has a single red gene, while a female has two. Red dominates black, meaning that a cat having an O gene will always have red coloring. Like black, red is also affected by the dilution gene. For male cats, we have the following two possible red colors (here, the black genes have no effect on the coat color):
D-O: Red |
ddO: Cream |
For female cats the situation gets a bit more complicated. If the female has two O genes she will be be red, with variations depending on the dilution gene in exactly the same way as for male red cats:
D-OO: Red |
ddOO: Cream |
However, a female cat with the Oo combination will have a partially black, partially red, coat. These cats are known as Torties (Tortoiseshells), and named after both their coat colours, starting with the black. The four possible Tortie colorings are thus as follows:
B-D-Oo: Black-Red Tortie |
B-ddOo: Blue-Cream Tortie |
bbD-Oo: Chocolate-Red Tortie |
bbddOo: Lilac-Cream Tortie |
When a pair of cats have kittens, the offspring will get a random set of genes from their parents according to the following simple process: for each gene, independently, one of the copies is selected uniformly at random from the father’s two copies, and the other copy is selected uniformly at random from the mother’s two copies. For the red gene, there is a $50\% $ chance that the offspring will be female in which case it will get the father’s red gene (and one of the mother’s red genes at random), and a $50\% $ chance that the offspring will be male in which case it will only get one of the mother’s red genes (at random).
Write a program which, given the colors of two cats, computes the most likely color for their offspring. For cats having a color where some genes do not affect the color, assume that the corresponding genes are uniformly random (over the two choices dominant/recessive). For example, if a cat is red, you should assume that the possibilities “DD” and “Dd” for the dilution gene are equally likely, and that the four possibilities “BB”, “Bb”, “bB” and “bb” are equally likely for the black gene (but note that “Bb” and “bB” are equivalent).
Input
The input consists of two lines. The first line gives the color of the female cat, and the second line gives the color of the male cat. Each color is spelled and capitalized exactly as when it is listed above, and the color is valid (i.e., the male cat won’t be a Tortie).
Output
Output a list of the possible color outcomes for the offspring of the two cats. Each line should contain a color followed by a number $0 < p \le 1$ indicating the probability of this particular outcome.
The list should be sorted first in decreasing order by probability, then in alphabetic order by name (see sample input 3 below). You do not need to worry about the precise formatting of the probabilities (e.g., number of decimals), but the absolute error of each probability must be smaller than $10^{-9}$.
Sample Input 1 | Sample Output 1 |
---|---|
Red Red |
Red 0.937500000 Cream 0.062500000 |
Sample Input 2 | Sample Output 2 |
---|---|
Lilac-Cream Tortie Blue |
Blue 0.375000000 Cream 0.250000000 Blue-Cream Tortie 0.187500000 Lilac 0.125000000 Lilac-Cream Tortie 0.062500000 |
Sample Input 3 | Sample Output 3 |
---|---|
Blue Red |
Black 0.328125000 Black-Red Tortie 0.328125000 Blue 0.109375000 Blue-Cream Tortie 0.109375000 Chocolate 0.046875000 Chocolate-Red Tortie 0.046875000 Lilac 0.015625000 Lilac-Cream Tortie 0.015625000 |