题解 | 有效括号序列

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param s string字符串 
# @return bool布尔型
#
class Stack:
    def __init__(self) -> None:
        self.items = []
 
    def push(self, x):
        self.items.append(x)
 
    def pop(self):
        if not self.is_empty():
            self.items.pop()
 
    def is_empty(self):
        return len(self.items) == 0
 
    def peek(self):  # 修正拼写
        if not self.is_empty():
            return self.items[-1]
        return None

class Solution:
    def isValid(self , s: str) -> bool:
        # write code here
        stack = Stack()
        for char in s:
            if char in "([{":
                stack.push(char)
            elif char in ")]}":
                if stack.is_empty():
                    return False
                elif char == ")" and stack.peek() == "(":
                    stack.pop()
                elif char == "}" and stack.peek() == "{":
                    stack.pop()
                elif char == "]" and stack.peek() == "[":
                    stack.pop()
                else:
                    return False
        if stack.is_empty():
            return True
        else:
            return False