栈stack

栈

LIFO: last in first out
#include <stack>
stack<char> ss;
ss.push();  
ss.pop();
ss.top();
ss.empty();

//括号匹配问题：法一（栈思想）

#include <iostream>
#include <stack>
#include <cstring>
using namespace std;
int n, flag = 1;
char s[100];
stack<char> ss;

int main() {
    cin >> n;
    while (n--) {
        cin >> s;
        for (int i = 0; i < strlen(s); i++) {//char[n]: strlen(s)
            if (s[i] == '{' || s[i] == '[' || s[i] == '(')//是否为左括号
                ss.push(s[i]);
            else if (ss.empty()) {//右括号开始匹配：栈空
                flag = 0;
                break;//直接跳出整个过程
            } else {//右括号开始匹配：栈非空，栈顶元素匹配
                switch (s[i]) {
                    case '}' :
                        if (ss.top() == '{') ss.pop();//记得弹出ss.pop()
                        break;//记得break;
                    case ']' :
                        if (ss.top() == '[') ss.pop();//区分ss.top() & ss.pop()
                        break;
                    case ')' :
                        if (ss.top() == '(') ss.pop();
                        break;
                }
            }
        }
        if (!ss.empty()) flag = 0;//判断栈空否
        while (!ss.empty()) ss.pop();
        if (flag) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
    return 0;
}