856. Score of Parentheses

题目

Given a balanced parentheses string S, compute the score of the string based on the following rule:

() has score 1 AB has score A + B, where A and B are balanced parentheses strings. (A) has score 2 * A, where A is a balanced parentheses string.

Example 1:

Input: "()"
Output: 1

Example 2:

Input: "(())"
Output: 2

Example 3:

Input: "()()"
Output: 2

Example 4:

Input: "(()(()))"
Output: 6

Note:

按照以下规则计算括号的分数：() 代表 1 分。AB 代表 A + B，A 和 B 分别是已经满足匹配规则的括号组。(A) 代表 2 * A，其中 A 也是已经满足匹配规则的括号组。给出一个括号字符串，要求按照这些规则计算出括号的分数值。

按照括号匹配的原则，一步步的计算每个组合的分数入栈。遇到题目中的 3 种情况，取出栈顶元素算分数。