UVA

//利用栈来解析表达式 //本题表达式比较简单，可以用一个栈来完成；遇到字母时入栈，遇到右括号时出栈并计算，然后结果入栈。因为输入保证合法，括号无须入栈 #include <iostream>#include <string>#include <stack>#include <cctype>using namespace std;struct Martrix{int a, b;Martrix(int a = 0, int b = 0):a(a), b(b){}} m[26];stack<Martrix>s;int main(){int n;cin >> n;for (int i = 0; i < n; i++){string name;cin >> name;int k = name[0] - 'A';cin >> m[k].a >> m[k].b;}string expr;while (cin >> expr){int len = expr.length();int error = 0, ans = 0;for (int i = 0; i < len; i++){char &tp = expr[i]; //tp is short for temp if (isalpha(tp)) s.push(m[tp - 'A']);else if (tp == ')'){Martrix m2 = s.top(); s.pop();Martrix m1 = s.top(); s.pop();if (m1.b != m2.a){error = 1; break;}ans += m1.a * m1.b * m2.b;s.push(Martrix(m1.a, m2.b));}}if (error) cout << "error" << endl;else cout << ans << endl;}return 0;}