856. Score of Parentheses

/*
 * @lc app=leetcode id=856 lang=cpp
 *
 * [856] Score of Parentheses
 *
 * https://leetcode.com/problems/score-of-parentheses/description/
 *
 * algorithms
 * Medium (63.90%)
 * Likes:    5526
 * Dislikes: 229
 * Total Accepted:    205.7K
 * Total Submissions: 322.7K
 * Testcase Example:  '"()"'
 *
 * Given a balanced parentheses string s, return the score of the string.
 *
 * The score of a balanced parentheses string is 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: s = "()"
 * Output: 1
 *
 *
 * Example 2:
 *
 *
 * Input: s = "(())"
 * Output: 2
 *
 *
 * Example 3:
 *
 *
 * Input: s = "()()"
 * Output: 2
 *
 *
 *
 * Constraints:
 *
 *
 * 2 <= s.length <= 50
 * s consists of only '(' and ')'.
 * s is a balanced parentheses string.
 *
 *
 */

// @lc code=start
class Solution {
public:
    int scoreOfParentheses(string s) {
        int res = 0;
        stack<int> stk;
        for (auto c : s) {
            if(c == '(') {
                stk.push(res);
                res = 0;
            } else {
                if (res == 0) {
                    res = 1 + stk.top();
                } else {
                    res = res * 2 + stk.top();
                }
                stk.pop();
            }
        }
        return res;
    }
};
// @lc code=end