Question

我必须创建一个包含两个数字（n和k）并返回其二项式系数的递归函数。

我必须使用pascal :: Int-> Int-> Int

老实说，我不明白哪里出了问题，谢谢您的帮助！

pascal :: Int -> Int -> Int
pascal n k
      | k == 0 = 1
      | n == n = 1
      | k > n  = 0
      | otherwise = pascal(n-1)(k-1) + pascal(n-1) + k

以下错误是：

main.hs:7:40: error:
    • Couldn't match expected type ‘Int’ with actual type ‘Int -> Int’
    • Probable cause: ‘pascal’ is applied to too few arguments
      In the second argument of ‘(+)’, namely ‘pascal (n - 1)’
      In the first argument of ‘(+)’, namely
        ‘pascal (n - 1) (k - 1) + pascal (n - 1)’
      In the expression: pascal (n - 1) (k - 1) + pascal (n - 1) + k
  |
7 |       | otherwise = pascal(n-1)(k-1) + pascal(n-1) + k
  |                                        ^^^^^^^^^^^
<interactive>:3:1: error:
    • Variable not in scope: main
    • Perhaps you meant ‘min’ (imported from Prelude)

Answer 1

正如异常所言，pascal (n-1)并没有多大意义，因为这是一个函数Int -> Int，所以不能将pascal (n-1) (k-1)和pascal (n-1)一起添加。

因此，您需要传递一个额外的参数。例如：

pascal :: Int -> Int -> Int
pascal _ 0 = 1
pascal n k
      | k == n = 1
      | k > n = 0
      | otherwise = pascal (n-1) (k-1) + pascal (n-1) k

请注意条件n == n始终为真，您可能想说n == k？

Haskell Pascal的三角形

1 个答案: