haskell - 在 preorder 和 inorder 之后用两个列表重建二叉树

问题描述

--给出了两个列表，一个按前序排序，另一个按中序排序。这两个列表来自同一个二叉树。对于这两个列表，二叉树是 --reconstructed。

——我在网上没有找到“排名”这个功能。我的教授告诉我们，函数“rank”可以输出一个元素在列表中的位置。

错误发生在使用函数“rank”的以下行中。

所以我有两个问题。

“排名”功能如何？
表达式“reconstruct :: [Int]->IntTree”是否正确？我不知道。

main :: IO ()    -- This says that main is an IO action.
main = return () -- This tells main to do nothing

data IntTree = Empty | Branch IntTree Int IntTree deriving (Show, Eq)

reconstruct :: [Int]->IntTree
--  Pattern matching 
reconstruct (x:xs) y = Branch (reconstruct take((rank x y) xs) take ((rank x y) y)) x x (reconstruct drop ((rank x y)+1 xs) drop ((rank x y)+1 y))

修正后

import Data.List


main :: IO ()    -- This says that main is an IO action.
main = return () -- This tells main to do nothing

data IntTree = Empty | Branch IntTree Int IntTree deriving (Show, Eq)

--Two lists are given, one sorted by preorder, the other sorted by inorder. 
-- And the two lists are from the same binary tree. With the two lists the binary tree is reconstructed.

reconstruct :: [Int]->[Int]->IntTree
--  Pattern matching 
reconstruct [] [] = Empty
reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))
    where p = span (x/=) y 

reconstruct _ _ = error "incomplete pattern"

错误


E:\Haskell\Uebungsblatt_2_Aufgabe_1.hs:15:32: error:
    * Couldn't match expected type `[Int] -> IntTree'
                  with actual type `IntTree'
    * The function `reconstruct' is applied to three arguments,
      but its type `[Int] -> [Int] -> IntTree' has only two
      In the first argument of `Branch', namely
        `(reconstruct take (length (fst p) xs) (fst p))'
      In the expression:
        Branch
          (reconstruct take (length (fst p) xs) (fst p))
          x
          (reconstruct drop (length (fst p) xs) (snd p))
   |
15 | reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))

   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

E:\Haskell\Uebungsblatt_2_Aufgabe_1.hs:15:44: error:
    * Couldn't match expected type `[Int]'
                  with actual type `Int -> [a0] -> [a0]'
    * Probable cause: `take' is applied to too few arguments
      In the first argument of `reconstruct', namely `take'
      In the first argument of `Branch', namely
        `(reconstruct take (length (fst p) xs) (fst p))'
      In the expression:
        Branch
          (reconstruct take (length (fst p) xs) (fst p))
          x
          (reconstruct drop (length (fst p) xs) (snd p))
   |
15 | reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))

   |                                            ^^^^

E:\Haskell\Uebungsblatt_2_Aufgabe_1.hs:15:50: error:
    * Couldn't match expected type `[Int] -> [Int]'
                  with actual type `Int'
    * The function `length' is applied to two arguments,
      but its type `[Int] -> Int' has only one
      In the second argument of `reconstruct', namely
        `(length (fst p) xs)'
      In the first argument of `Branch', namely
        `(reconstruct take (length (fst p) xs) (fst p))'
   |
15 | reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))

   |                                                  ^^^^^^^^^^^^^^^^^

E:\Haskell\Uebungsblatt_2_Aufgabe_1.hs:15:81: error:
    * Couldn't match expected type `[Int] -> IntTree'
                  with actual type `IntTree'
    * The function `reconstruct' is applied to three arguments,
      but its type `[Int] -> [Int] -> IntTree' has only two
      In the third argument of `Branch', namely
        `(reconstruct drop (length (fst p) xs) (snd p))'
      In the expression:
        Branch
          (reconstruct take (length (fst p) xs) (fst p))
          x
          (reconstruct drop (length (fst p) xs) (snd p))
   |
15 | reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))

   |                                                                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

E:\Haskell\Uebungsblatt_2_Aufgabe_1.hs:15:93: error:
    * Couldn't match expected type `[Int]'
                  with actual type `Int -> [a1] -> [a1]'
    * Probable cause: `drop' is applied to too few arguments
      In the first argument of `reconstruct', namely `drop'
      In the third argument of `Branch', namely
        `(reconstruct drop (length (fst p) xs) (snd p))'
      In the expression:
        Branch
          (reconstruct take (length (fst p) xs) (fst p))
          x
          (reconstruct drop (length (fst p) xs) (snd p))
   |
15 | reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))

   |                                                                                             ^^^^

E:\Haskell\Uebungsblatt_2_Aufgabe_1.hs:15:99: error:
    * Couldn't match expected type `[Int] -> [Int]'
                  with actual type `Int'
    * The function `length' is applied to two arguments,
      but its type `[Int] -> Int' has only one
      In the second argument of `reconstruct', namely
        `(length (fst p) xs)'
      In the third argument of `Branch', namely
        `(reconstruct drop (length (fst p) xs) (snd p))'
   |
15 | reconstruct (x:xs) y = Branch (reconstruct take (length (fst p) xs) (fst p)) x (reconstruct drop (length (fst p) xs) (snd p))

   |                                                                                                   ^^^^^^^^^^^^^^^^^
[Finished in 0.5s]

标签： haskell

haskell - 在 preorder 和 inorder 之后用两个列表重建二叉树

问题描述

解决方案

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