Question

如何修改此代码以接受不同长度的列表？

修改函数rippleCarryAdder以接受不同长度的列表。例如，调用（rippleCarryAdder [true] [false; true]）应该求值为（[true; false]，false），即1 + 01求值为2且没有溢出。

let xor a b = (a || b) && (not (a && b))

(* fullAdder : bool -> bool -> bool -> (bool * bool)
 *
 * The call (fullAdder a b carryIn) adds the bits a, b and carryIn
 * producing the sum and the carry out.
 *)
let fullAdder a b cin =
  let c = xor a b in
  let sum = xor c cin in
  let carryOut = (c && cin) || (a && b)
  in
  (sum, carryOut)

(* rippleCarryAdder : bool list -> bool list -> bool -> (bool list * bool)
 *
 * The call (rippleCarryAdder ms ns carryIn) implements a ripple carry
 * adder. 
 *)
let rippleCarryAdder ms ns =
  let rec repeat ms ns carryIn acc =
    match (ms, ns) with
    | ([], []) -> (acc, carryIn)
    | (m::ms, n::ns) -> let (sum, carryOut) = fullAdder m n carryIn
            in
            repeat ms ns carryOut (sum::acc)
  in
  repeat (List.rev ms) (List.rev ns) false []

Answer 1

let fill_in a (ms,ns) =
  let rec fill_left a = function
      ([],[])          -> []
    | ([],_::ns)       -> a::fill_left a ([],ns)
    | (m::ms,[])       -> m::fill_left a (ms,[])
    | (m::ms,_::ns)    -> m::fill_left a (ms,ns)
  in
  let rec fill_right a = function
      ([],[])          -> []
    | (_::ms,[])       -> a::fill_right a (ms,[])
    | ([],n::ns)       -> n::fill_right a ([],ns)
    | (_::ms,n::ns)    -> n::fill_right a (ms,ns)
  in
  (fill_left a (ms,ns),fill_right a (ms,ns))

let rippleCarryAdder2 ms ns =
  let (ms,ns)=fill_in false (List.rev ms,List.rev ns) in
  rippleCarryAdder (List.rev ms) (List.rev ns)

测试：

# fill_in false ([true;false],[true;false;true;true]);;
- : bool list * bool list =
([true; false; false; false], [true; false; true; true])

# fill_in 0 ([1;1;0;1],[2;3]);;
- : int list * int list = ([1; 1; 0; 1], [2; 3; 0; 0])

# rippleCarryAdder2 [true] [false;true];;
- : bool list * bool = ([true; false], false)

OCaml：rippleCarryAdder具有不同长度的输入

1 个答案: