Indices of Enclosing Parentheses | Dataford Interview Questions

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Problem

The Outreach sequence editor supports parenthesized template expressions. Given a balanced string and the index of a non-parenthesis character, return the indices of the innermost pair of parentheses that strictly encloses that character.

If the character is not enclosed by any parentheses, return [-1, -1].

Formal Specification

Implement find_enclosing_parentheses(s, target_index):

s is a string containing lowercase letters, spaces, and parentheses.
target_index is a valid index of a non-parenthesis character in s.
The parentheses in s are balanced and properly nested.
Return [open_index, close_index] for the innermost enclosing pair, where open_index < target_index < close_index.
Return [-1, -1] when no pair encloses the target.

Constraints

1 <= len(s) <= 10^5
0 <= target_index < len(s)
s[target_index] is not '(' or ')'
s contains balanced, properly nested parentheses

Function Signature

def find_enclosing_parentheses(s, target_index):