Question

我是Haskell的初学者。我在书中发现了一个问题：检查列表是否具有“山”的方面，升序元素 - 降序元素。检查列表是否具有“谷”的方面，降序元素 - 升序元素。请帮助我。

例：

“山”：[1,2,3,4,5,6,3,2,1]

“山谷”：[4,3,2,1,1,2,3,4]

我的代码看起来：

山

ordered::[Int]->Bool
ordered [a]=True
ordered (a:l)=if(a>head(l)) then False
          else ordered(l)

谷

ordered::[Int]->Bool
ordered [a]=True
ordered (a:l)=if(a<head(l)) then False
          else ordered(l)

Answer 1

您应该首先考虑基本情况。您已经开始使用包含1个元素的列表的基本案例，但是有一个更简单的基本案例：空列表。空列表通常被视为升序和降序。接下来你要做的就是退出head。它是偏袒的，会引导你犯错误。相反，模式匹配所有内容。

在编写一个非常简单的版本之后，在编写模式匹配版本之后提示：使用zipWith和drop。请注意，与tail不同，drop是一个总函数。

Answer 2

localMinima :: [Integer] -> Integer
localMinima [x]=x
localMinima (x:xs) = if x<m then x
                 else m where m=localMinima xs


rmAdjacentDups :: [Integer]->[Integer]
rmAdjacentDups []     = []
rmAdjacentDups (x:xs) = x : (rmAdjacentDups $ dropWhile (== x) xs)


isValley :: [Integer] -> Bool
isValley xs = 1 == (length $ localMinima $ rmAdjacentDups xs)

Answer 3

这是一个策略：如果删除相邻的重复元素后，列表只有一个local maximum，则列表为“山峰”。同样，“谷”是一旦删除相邻重复元素就只有一个局部最小值的列表。下面的函数将告诉列表是山还是山谷：

from tkinter import *
myGui=Tk()
myGui.geometry("800x600")
myGui.title("Pete's Pizza Parlour~Order Form")

#TOPPING SELECTION
toppings_lbl=Label(myGui,text="Toppings:",font=("Good Times",10),fg="blue").pack()
a=IntVar()
olives_chk=Checkbutton(myGui,text="Olives",variable=a).pack()
b=IntVar()
tomatoes_chk=Checkbutton(myGui,text="Tomatoes",variable=b).pack()
c=IntVar()
pepperoni_chk=Checkbutton(myGui,text="Pepperoni",variable=c).pack()
d=IntVar()
hotPeppers_chk=Checkbutton(myGui,text="Hot Peppers",variable=d).pack()
e=IntVar()
onions_chk=Checkbutton(myGui,text="Onions",variable=e).pack()
f=IntVar()
ham_chk=Checkbutton(myGui,text="Ham",variable=f).pack()
g=IntVar()
sausage_chk=Checkbutton(myGui,text="Sausage",variable=g).pack()
h=IntVar()
greenPeppers_chk=Checkbutton(myGui,text="Green Peppers",variable=h).pack()

olivesSelectionStr="olives"
tomatoesSelectionStr="tomatoes"
pepperoniSelectionStr="pepperoni"
hotPeppersSelectionStr="hot peppers"
onionsSelectionStr="onions"
hamSelectionStr="ham"
sausageSelectionStr="sausage"
greenPeppersSelectionStr="green peppers"
noToppingsStr="no toppings."


def checkToppings():
    toppingsList=""
    olivesSelection=a.get()
    tomatoesSelection=b.get()
    pepperoniSelection=c.get()
    hotPeppersSelection=d.get()
    onionsSelection=e.get()
    hamSelection=f.get()
    sausageSelection=g.get()
    greenPeppersSelection=h.get()
    if(olivesSelection==1):
        toppingsList=toppingsList+olivesSelectionStr
    if(tomatoesSelection==1):
        toppingsList=toppingsList+tomatoesSelectionStr
    if(pepperoniSelection==1):
        toppingsList=toppingsList+pepperoniSelectionStr
    if(hotPeppersSelection==1):
        toppingsList=toppingsList+hotPeppersSelectionStr
    if(onionsSelection==1):
        toppingsList=toppingsList+onionsSelectionStr
    if(hamSelection==1):
        toppingsList=toppingsList+hamSelectionStr
    if(sausageSelection==1):
        toppingsList=toppingsList+sausageSelectionStr
    if(greenPeppersSelection==1):
        toppingsList=toppingsList+greenPeppersSelectionStr
    if toppingsList=="":
        toppingsList=noToppingsStr
    print(toppingsList)

topping_btn = Button(myGui,text='print toppings', command = checkToppings)
topping_btn.pack()
myGui.mainloop()

如果您实施isMountain :: [Integer] -> Bool isMountain xs = 1 == (length $ localMaxima $ rmAdjacentDups xs) isValley :: [Integer] -> Bool isValley xs = 1 == (length $ localMinima $ rmAdjacentDups xs) *Main> isMountain [1,2,3,4,5,6,3,2,1] True *Main> isMountain [1,2,3,4,5,6,5,6,3,2,1] False *Main> isValley [4,3,2,1,1,2,3,4] True *Main> isValley [4,3,2,1,2,1,1,2,3,4] False，localMaxima或localMinima，请发表评论。希望这有帮助！

检查列表是否具有升序元素 - 降序元素或降序元素 - 升序元素

3 个答案: