esercizi.ml

type col = Rosso | Giallo | Verde | Blu
type 'a col_assoc = (col * 'a list) list
type 'a tree = Empty | Tr of 'a * 'a tree * 'a tree

let colore x lst = fst (List.find (fun (a,b) -> List.mem x b) lst)

let next = function
    | Rosso | Giallo | Verde -> Blu
    | Blu -> Rosso

let path_to k colori =
    let rec aux c sol = function
        | Empty -> raise Fail
        | Tr(x,_,_) when (colore x colori)=c -> raise Fail
        | Tr(x,Empty,Empty) -> if x=k then (List.rev (x::sol)) else raise Fail
        | Tr(x,lt,rt) -> let c,s = (colore x colori),(x::sol) in
                         try aux c s lt with _ -> aux c s rt
    in function
        | Tr(x,_,_) as t -> aux (next (colore x colori)) [] t
        | Empty -> raise Fail