Question

我必须编写一个函数，它将找到二叉树中所有元素的总和。

这是如何定义的（树）：

datatype 'a tree= Leaf of 'a | Node of 'a tree * 'a * 'a tree

我不知道该怎么做。我承认我是SML的初学者。

例如：sumTree (Node (Node (Leaf 1, 3, Leaf 2), 7, Leaf 4))应返回17. sumTree是函数名称。

感谢您的帮助。

Answer 1

我希望你花点时间了解这一点。如果您对此有任何疑问，请与我们联系：

(*
 * This is a recursive datatype, because the Node constructor contains two
 * elements of type `tree`, the type which we're currently defining.
 *)
datatype 'a tree =
    Leaf of 'a
  | Node of 'a tree * 'a * 'a tree

(*
 * Notice how the structure of the `sumTree` function follows the structure
 * of the `tree` datatype. But `tree` is a recursive datatype, which means
 * that `sumTree` will probably be a recursive function. This is called
 * structural recursion. We recurse accordingly to the structure of the type.
 *)
fun sumTree (Leaf n) = n
  | sumTree (Node (left, n, right)) = (sumTree left) + n + (sumTree right)

基本思想是为简单案例（Leaf）解决问题，在复杂案例中（Node）依赖于简单案例的解决方案。

二叉树的SML和

1 个答案: