方法思路

1. 栈的应用：使用栈来检查括号的有效性。遇到左括号时压栈，遇到右括号时检查栈顶是否匹配。
2. 计数有效括号对：在每次成功匹配一对括号时，增加计数器。
3. 最终检查：遍历完字符串后，栈应为空，否则说明有未匹配的括号。

代码实现

Java

import java.io.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int t = Integer.parseInt(br.readLine());
        
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < t; i++) {
            String s = br.readLine();
            sb.append(isValidBrackets(s)).append("\n");
        }
        System.out.print(sb);
    }
    
    static String isValidBrackets(String s) {
        char[] stack = new char[s.length()];
        int top = -1;
        int count = 0;
        
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            switch (c) {
                case '(': case '{': case '[':
                    stack[++top] = c;
                    break;
                case ')':
                    if (top < 0 || stack[top--] != '(') return "False";
                    count++;
                    break;
                case '}':
                    if (top < 0 || stack[top--] != '{') return "False";
                    count++;
                    break;
                case ']':
                    if (top < 0 || stack[top--] != '[') return "False";
                    count++;
                    break;
            }
        }
        
        return (top == -1) ? String.valueOf(count) : "False";
    }
}

Python

def is_valid_brackets(s):
    stack = []
    pairs = {')': '(', '}': '{', ']': '['}
    count = 0
    
    for char in s:
        if char in '({[':
            stack.append(char)
        elif char in ')}]':
            if not stack or stack.pop() != pairs[char]:
                return False
            count += 1
    
    return count if not stack else False

t = int(input())
for _ in range(t):
    s = input().strip()
    result = is_valid_brackets(s)
    print(result)

C++

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

string isValidBrackets(string s) {
    stack<char> st;
    unordered_map<char, char> pairs = {{')', '('}, {'}', '{'}, {']', '['}};
    int count = 0;
    
    for (char c : s) {
        if (c == '(' || c == '{' || c == '[') {
            st.push(c);
        } else if (c == ')' || c == '}' || c == ']') {
            if (st.empty() || st.top() != pairs[c]) {
                return "False";
            }
            st.pop();
            count++;
        }
    }
    
    if (st.empty()) {
        return to_string(count);
    } else {
        return "False";
    }
}

int main() {
    int t;
    cin >> t;
    cin.ignore();
    
    for (int i = 0; i < t; i++) {
        string s;
        getline(cin, s);
        cout << isValidBrackets(s) << endl;
    }
    
    return 0;
}