Play With Strings

You are given a string $s$ of length $N$ and three values $A,B,C$. The numeric of a character is defined as (index in English Alphabet)%3 (For eg. 0 for 'a', 1 for 'b' , 2 for 'c' , 0 for 'd' .....). Now you have to assign $A,B,C$ to each of the three possible numeric i.e. $0,1,2$ in any random order, such that each $A,B,C$ is assigned to exactly one of the numeric and at least one value from $A