leetcode20-Valid Parentheses有效的括号

利用栈

编程方式一：按照课本上思路改写的

class Solution:
    def isValid(self, s: str) -> bool:
        map={'(':')','[':']','{':'}'}
        match=True
        i=0
        stack=[]
        while i<len(s) and match:
            if s[i] in "([{":
                stack.append(s[i])
            else:
                if len(stack)==0:
                    match=False
                else:
                    open=stack.pop()
                    if s[i]!=map[open]:#s[i] is close symbol
                        match=False
            i=i+1
        if len(stack)!=0:
            match=False
        return match

编程方式二：leetcode官方解答 ,更加简洁

class Solution:
    def isValid(self, s: str) -> bool:
        stack=[]
        mapping={')':'(',']':'[','}':'{'}
        for char in s:
            if char in mapping:
                top=stack.pop() if stack else '#'   #防止stack为空时报错
                if mapping[char] != top:
                    return False
            else:
                stack.append(char)
        return not stack