题解 | #矩阵乘法计算量估算#

import java.util.Scanner;
import java.util.Stack;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            // 要计算的矩阵个数
            int n = scanner.nextInt();
            // 数组，存储每个矩阵的行数，列数
            int[][] arr = new int[n][2];
            for (int i = 0; i < n; i++) {
                arr[i][0] = scanner.nextInt();
                arr[i][1] = scanner.nextInt();
            }
            scanner.nextLine();
            // 计算法则
            String str = scanner.nextLine();
            System.out.println(timesOfMatrixMultiplication(str, arr));
        }
    }

    private static int timesOfMatrixMultiplication(String str, int[][] arr) {
        // 需要进行的乘法次数
        int total = 0;
        Stack<Integer> stack = new Stack<>();
        for (char c : str.toCharArray()) {
            if (c != '(') {
                if (c == ')') {
                    int x = stack.pop();
                    int y = stack.pop();
                    total += arr[y][0] * arr[y][1] * arr[x][1];
                    arr[y][1] = arr[x][1];
                    stack.add(y);
                } else {
                    int i = c - 'A';
                    stack.add(i);
                }
            }
        }

        return total;
    }
}