题目

地址

https://leetcode.com/problems/valid-parentheses/description/

内容

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.
3. 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

Example 4:

Input: s = “([])”
Output: true

Constraints:

• 1 <= s.length <= 10⁴
• s consists of parentheses only ‘()[]{}’.

解题

这题就是要求检测各种括号的匹配问题。我记得上大学时，老师讲栈结构时，就是用类似的题目来考察我们的。对于([{，我们就入栈；对于)]}，我们就检测栈顶的括号类型是否匹配。一旦发现不匹配，就直接返回false。只有在分析完所有字符后，栈的空间大小是0，才能说明输入的内容是合法的。

#include <string>
#include <stack>
using namespace std;

class Solution {
public:
    bool isValid(string s) {
        stack<char> charStack;
        for(char ch : s) {
            if(ch == '(' || ch == '[' || ch == '{') {
                charStack.push(ch);
            } else {
                if (charStack.empty()) {
                    return false;
                }
                char topChar = charStack.top();
                if ((ch == ')' && topChar != '(') || 
                    (ch == ']' && topChar != '[') || 
                    (ch == '}' && topChar != '{')) {
                    return false;
                }
                charStack.pop();
            }
        }
        return charStack.empty();
    }
};

代码地址

https://github.com/f304646673/leetcode/tree/main/20-Valid-Parentheses