题解 | #矩阵乘法计算量估算#

#include <cctype>
#include <iostream>
#include <stack>
#include <vector>
using namespace std;

int main() {
    int n;
    while (cin >> n) {
        vector<pair<int, int>> sz(n);
        for(int i=0;i<n;i++){
            cin>>sz[i].first>>sz[i].second;
        }
        string s;
        cin>>s;
        int ret = 0;
        stack<pair<int, int>> stk;
        for(int i=0;i<s.size();i++){
            if(s[i]==')'){
                auto y = stk.top();
                stk.pop();
                auto x = stk.top();
                stk.pop();
                ret+=x.first*x.second*y.second;
                stk.push({x.first, y.second});
            }
            else if(s[i]!='('){
                int k = s[i]-'A';
                stk.push(sz[k]);
            }
        }
        cout<<ret;
    }
}