Valid parentheses-优快云博客

本文链接：https://blog.youkuaiyun.com/ray_kong/article/details/130045850

文章提供了一种使用栈数据结构来检查给定字符串中括号是否有效的C++和Python代码实现。在C++解决方案中，通过压栈处理开括号，然后匹配相应的闭括号；Python方案则使用replace函数，但效率较低。有效输入字符串需满足括号正确配对且顺序正确。

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一、问题描述

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

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Every close bracket has a corresponding open bracket of the same type.

Example 1:

Input: s = "()"
Output: true
Example 2:

Input: s = "()[]{}"
Output: true
Example 3:

Input: s = "(]"
Output: false

二、代码

符号匹配问题，选择用栈解决。

C++：

class Solution {
public:
    bool isValid(string s) {
        if(s.length() % 2 != 0) return false;
        stack<char> stack_s;
        for (int i=0;i<s.length();i++){
            if(s[i]=='(') stack_s.push(')');//把对应的符号压入栈
            else if(s[i]=='{') stack_s.push('}');
            else if(s[i]=='[') stack_s.push(']');
            else if(stack_s.empty()|| stack_s.top() != s[i])return false;
            else stack_s.pop();//遇到对应的符号就压出
        }
        return stack_s.empty();//判断标志
    }
};

python：利用replace()函数，代价较大。原因在于replace函数内部需要进行符号匹配。

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        while '()' in s or '{}' in s or '[]' in s:
            s = s.replace('()', '')
            s = s.replace('{}', '')
            s = s.replace('[]', '')
        return s == ''