Question

问题是检查字符串中的括号是否正确关闭。对于Haskell实现，到目前为止我有以下内容。看起来很尴尬。我正在寻找更多＆＃34; Haskell风格＆＃34;或更优雅的实施。

import Data.List

isValidParentheses :: String -> Bool
isValidParentheses = isValidHelper . (filter isParenthese)

getIndex :: (Eq a) => a -> [a] -> Int
getIndex c xs =  getOut (elemIndex c xs)
  where getOut (Just x) = x
        getOut Nothing = -1

isLeftParenthese :: Char -> Bool
isLeftParenthese c = (getIndex c "{[(") /= -1

isRightParenthese :: Char -> Bool
isRightParenthese c = (getIndex c "}])") /= -1

isParenthese :: Char -> Bool
isParenthese c = isLeftParenthese c || isRightParenthese c


isValidHelper :: String -> Bool
isValidHelper xs = helper xs []
  where helper (x:xs) []     | isRightParenthese x = False
                             | otherwise = helper xs [x]
        helper [] st = null st
        helper (x:xs) (s:ss) | isLeftParenthese x = helper xs (x:s:ss)
                              | ((getIndex x "}])") /= (getIndex s "{[(")) = False
                              | otherwise = helper xs ss

由于

Answer 1

循环播放字符串
在堆栈中存储左括号
将匹配的括号弹出堆栈

检查堆栈末尾是否为空

isValid = loop []
  where
    match '(' ')' = True
    match '{' '}' = True
    match '[' ']' = True
    match  _   _  = False

    loop st [] = null st
    loop st (x:xs)
      | x `elem` "([{" = loop (x:st) xs
      | x `elem` ")]}" = case st of
        open : st' | match open x -> loop st' xs
        _ -> False -- unmatched close
      | otherwise = loop st xs

字符串中的有效括号（Haskell实现）

1 个答案: