题解 | #矩阵乘法计算量估算#

import java.util.Scanner
import java.util.*


fun main(args: Array<String>) {
    val read = Scanner(System.`in`)
    val n = read.nextLine().toInt()
    val a = Array(n) {
        Array(2) {
            0
        }
    }
    for (i in 0 until n) {
        val res = read.nextLine().split(' ').map {
            it.toInt()
        }
        a[i][0] = res[0]
        a[i][1] = res[1]
    }
    val rule = read.nextLine()
    val stackVal = Stack<Pair<Int, Int>>()
    var sum = 0
    rule.forEach {
        if (it.isLetter()) {
            a[it - 'A'].apply {
                stackVal.push(Pair(get(0), get(1)))
            }
        } else {
            when (it) {
                ')' -> {
                    val curVal = stackVal.pop()
                    val preVal = stackVal.pop()
                    sum += preVal.first * curVal.second * preVal.second
                    stackVal.push(Pair(preVal.first, curVal.second))
                }
            }
        }
    }
    println(sum)
}