给定一个只包括 ‘(‘，‘)‘，‘{‘，‘}‘，‘[‘，‘]‘ 的字符串 s ，判断字符串是否有效。

有效字符串需满足：

1. 左括号必须用相同类型的右括号闭合。
2. 左括号必须以正确的顺序闭合。

Given a string s containing just the characters ‘(‘, ‘)‘, ‘{‘, ‘}‘, ‘[‘ and ‘]‘, determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

示例 1：

输入：s = "()"
输出：true

示例 2：

输入：s = "()[]{}"
输出：true

示例 3：

输入：s = "(]"
输出：false

示例 4：

输入：s = "([)]"
输出：false

示例 5：

输入：s = "{[]}"
输出：true

 提示：

• 1 <= s.length <= 104
• s 仅由括号 ‘()[]{}‘ 组成

题解一(python):

 1 class Solution:
 2     def isValid(self, s: str) -> bool:
 3         dic = {‘)‘:‘(‘,‘]‘:‘[‘,‘}‘:‘{‘} # 字典
 4         stack = []
 5         for i in s:
 6             if stack and i in dic: # 若栈不为空且i为有效字符串
 7                 if stack[-1] == dic[i]: # 若栈顶元素能和dic[i]匹配，则出栈
 8                     stack.pop()
 9                 else: 
10                     return False # 否则就返回false
11             else: 
12                 stack.append(i) # 若i在栈中无，则压栈
13             
14         return not stack