跟MT3033新的表达式类似，只多了一个括号合法性的判断

#include <bits/stdc++.h>
using namespace std;
const int N = 40;
bool tag[N];
bool is_op(char c)
{return c == '+' || c == '-' || c == '*' || c == '/' || c == '^';
}
int priority(char op)
{ // 优先级排序if (op == '+' || op == '-')return 1;if (op == '*' || op == '/')return 2;if (op == '^')return 3;return -1;
}
void process_op(stack<int> &st, char op)
{int r = st.top();st.pop();int l = st.top();st.pop();switch (op){case '+':st.push(l + r);break;case '-':st.push(l - r);break;case '*':st.push(l * r);break;case '/':st.push(l / r);break;case '^':st.push(pow(l, r));break;}
}int evaluate(string &s)
{stack<int> st;stack<char> op;for (int i = 0; i < s.size(); i++){if (s[i] == '('){if (!tag[i]){continue; // 括号位置不合法}op.push(s[i]);}else if (s[i] == ')'){if (!tag[i]){continue; // 括号位置不合法}while (op.top() != '('){process_op(st, op.top());op.pop();}op.pop();}else if (is_op(s[i])){ // 运算符优先级while (!op.empty() && priority(op.top()) >= priority(s[i])){process_op(st, op.top());op.pop();}op.push(s[i]);}else{int num = 0;while (i < s.size() && isdigit(s[i])){num = num * 10 + s[i] - '0';i++;}i--;st.push(num);}}while (!op.empty()){process_op(st, op.top());op.pop();}return st.top();
}void init(string &s)
{ // 去除多余的括号stack<pair<char, int>> st;for (int i = 0; i < s.size(); i++){if (!st.empty() && st.top().first == '(' && s[i] == ')'){                                         // 如果栈顶为(并且当前遍历到了(  --> 合法tag[i] = tag[st.top().second] = true; // 两个位置为true 即括号位置合法st.pop();                             // 合法的(弹出}else if (s[i] == '(') // 记录(位置{st.push({'(', i});}}
}int main()
{string s;cin >> s;init(s);cout << evaluate(s);return 0;
}