题解 | 矩阵乘法计算量估算

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

void compute(stack<int>& x, stack<int>& y, int& sum) {
    int a = x.top();
    x.pop();
    int b = y.top();
    y.pop();
    int c = x.top();
    y.pop();
    sum += a * b * c;
    y.push(b);
}

int main() {
    int n, x, y, sum = 0, t, ans = 0;
    cin >> n;
    string s;
    vector<vector<int>> v(n, vector<int>(2, 0));
    for (int i = 0; i < n; i++) {
        cin >> x >> y;
        v[i][0] = x;
        v[i][1] = y;
    }
    cin >> s;
    stack<int> xx;
    stack<int> yy;
    stack<int> kuohao;
    for (int i = 0; i < s.size(); i++) {
        if (s[i] == '(') {
            t++;
        } else if (s[i] == ')') {
            int q = kuohao.top();
            kuohao.pop();
            if (q == 1 && xx.size() != 1) {
                compute(xx, yy, sum);
            }
            else{
                q--;
                kuohao.push(q);
            }
        } else {
            if (t != 0) {
                xx.push(v[ans][0]);
                yy.push(v[ans][1]);
                ans++;
                kuohao.push(t);
                t = 0;
            } else {
                xx.push(v[ans][0]);
                yy.push(v[ans][1]);
                compute(xx, yy, sum);
                ans++;
            }
        }
    }
    cout << sum;
}
// 64 位输出请用 printf("%lld")