856. Score of Parentheses #

Problem #

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:

1. S is a balanced parentheses string, containing only ( and ).
2. 2 <= S.length <= 50

Problem Summary #

Calculate the score of parentheses according to the following rules: () represents 1 point. AB represents A + B, where A and B are both parenthesis groups that already satisfy the matching rules. (A) represents 2 * A, where A is also a parenthesis group that already satisfies the matching rules. Given a parentheses string, calculate the score value of the parentheses according to these rules.

Solution Approach #

According to the principle of parentheses matching, calculate the score of each combination step by step and push it onto the stack. When encountering the 3 cases in the problem, take out the top element of the stack to calculate the score.

Code #

package leetcode

func scoreOfParentheses(S string) int {
	res, stack, top, temp := 0, []int{}, -1, 0
	for _, s := range S {
		if s == '(' {
			stack = append(stack, -1)
			top++
		} else {
			temp = 0
			for stack[top] != -1 {
				temp += stack[top]
				stack = stack[:len(stack)-1]
				top--
			}
			stack = stack[:len(stack)-1]
			top--
			if temp == 0 {
				stack = append(stack, 1)
				top++
			} else {
				stack = append(stack, temp*2)
				top++
			}
		}
	}
	for len(stack) != 0 {
		res += stack[top]
		stack = stack[:len(stack)-1]
		top--
	}
	return res
}