T20 有效的括号

T20 有效的括号

题目描述：

思路：只需要判断当前括号是否与栈中的栈顶元素，当前括号如果是左括号直接放入，如果是右括号，如果不匹配则一定出错，如果匹配则只需要将匹配好的括号出栈，检查下一个元素即可。

代码如下：

class Solution:
    def isValid(self, s: str) -> bool:
        pstack = ["x"]
        for i in range(len(s)):              
            if s[i] == ")" and pstack[-1] == "(":
                pstack.pop()
            elif s[i] == ")" and pstack[-1] != "(":
                return False
            elif s[i] == "]" and pstack[-1] == "[":
                pstack.pop()
            elif s[i] == "]" and pstack[-1] != "[":
                return False                
            elif s[i] == "}" and pstack[-1] == "{":
                pstack.pop()
            elif s[i] == "}" and pstack[-1] != "{":
                return False
            else:
                pstack.append(s[i])

        return True if len(pstack)==1 else False

结果如下：

看了看代码，总觉得非常臃肿，于是改了一下，用字典存储了一下，不需要一个个写判断了，代码如下：

class Solution:
    def isValid(self, s: str) -> bool:
        mydict = {")":"(","]":"[","}":"{"}
        pstack = ["x"]
        for i in range(len(s)):  
            if s[i] in mydict:
                if pstack[-1] == mydict[s[i]]:
                    pstack.pop()
                else:
                    return False
            else:
                pstack.append(s[i])
        return True if len(pstack)==1 else False

结果如下所示：