题解 | #矩阵乘法计算量估算#
矩阵乘法计算量估算
https://www.nowcoder.com/practice/15e41630514445719a942e004edc0a5b?tpId=37&tqId=21293&rp=1&ru=/exam/oj/ta&qru=/exam/oj/ta&sourceUrl=%2Fexam%2Foj%2Fta%3FtpId%3D37&difficulty=3&judgeStatus=undefined&tags=&title=
n = int(input())
a = [0] * n
b = [0] * n
for i in range(n):
a[i], b[i] = map(int, input().split(" "))
s = input()
ans = 0
stack = []
for ch in s:
if ch == ')':
b1, b2 = stack.pop()
a1, a2 = stack.pop()
ans += a1 * a2 * b2
stack.append([a1, b2])
elif ch != '(':
idx = ord(ch) - ord('A')
stack.append([a[idx], b[idx]])
print(ans)
