LeetCode-020 Valid Parentheses_given a string s containing just the characters '(-优快云博客

本文介绍了一个简单的算法，用于验证输入字符串中的括号是否正确匹配。该算法使用栈数据结构来跟踪括号，并确保它们按正确的顺序关闭。文章通过几个示例展示了如何判断括号序列的有效性。

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Description

Given a string 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.
Note that an empty string is also considered valid.

Example

Example 1:

Input: “()”
Output: true

Example 2:

Input: “()[]{}”
Output: true

Example 3:

Input: “(]”
Output: false

Example 4:

Input: “([)]”
Output: false

Example 5:

Input: “{[]}”
Output: true

Analyse

括号匹配，栈的基本操作，没什么好分析的。

Code

class Solution {
public:
    bool isValid(string s) {
        stack<char> check;
        for (int i = 0; i < s.length(); i++) {
            if (s[i] == '(' || s[i] == '[' || s[i] == '{') {
                check.push(s[i]);
            } else {
                if (check.size() == 0 ) return false;
                char top = check.top();
                if (s[i] == ')' && top == '(') check.pop();
                else if (s[i] == ']' && top == '[') check.pop();
                else if (s[i] == '}' && top == '{') check.pop();
                else return false;
            }
        }
        if (!check.empty()) return false;
        return true;
    }
};