September 27Medium

Reverse substrings between each pair of parentheses

String
Stack
Bracket Sequences

Problem

You are given a string s that consists of lower case English letters and brackets.

Reverse the strings in each pair of matching parentheses, starting from the innermost one.

Your result should not contain any brackets.

Solution

class Solution:
    def reverseParentheses(self, s: str) -> str:
        def get_inside(start, s):
            i = start + 1
            opened = 1
            inside_str = ""
            while opened:
                if s[i] == "(":
                    opened += 1
                elif s[i] == ")":
                    opened -= 1
                if opened:
                    inside_str += s[i]
                i += 1

            return inside_str

        def reverse(s):
            res = ""
            i = 0
            while i < len(s):
                if s[i] != "(":
                    res += s[i]
                else:
                    inside_str = get_inside(i, s)
                    res += reverse(inside_str)[::-1]
                    i += 1 + len(inside_str)
                i += 1
            return res
        
        return reverse(s)

# Or "the smart" solution

class Solution:
    def reverseParentheses(self, s: str) -> str:
        while "(" in s:
            s = re.sub(r'\((\w*)\)', lambda x: x.group(1)[::-1], s)
        return s