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Home/Questions/Python/Coding/Write a function to remove invalid parentheses from a string.

Write a function to remove invalid parentheses from a string.

Python/Codingeasy0.5 min readPremium

**BFS/DFS:** Remove min parentheses to make valid. BFS: try removing 1,2,... until valid. DFS with count: track balance, prune invalid. Return all valid results (BFS finds min removal). **Two-pass:** Count extra ( and ); remove in second pass....

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Frequency
Low
Asked at 1 company
Category
179
questions in Python/Coding
Difficulty Split
127E|24M|28H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Disney+ Hotstar

Why This Question Matters

This easy-level Python/Coding question appears frequently in data engineering interviews at companies like Disney+ Hotstar. While less common, it tests deeper understanding that distinguishes strong candidates.

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Expert Answer
94 words

BFS/DFS: Remove min parentheses to make valid. BFS: try removing 1,2,... until valid. DFS with count: track balance, prune invalid. Return all valid results (BFS finds min removal).

Two-pass: Count extra ( and ); remove in second pass. BFS guarantees minimum.

def remove_invalid(s):
def valid(s): balance=0; [balance:=balance+1 if c=='(' else (balance-1 if c==')' else balance) for c in s]; return balance==0
level = {s}
while level:
valid_set = [x for x in level if valid(x)]
if valid_set: return valid_set
level = {s[:i]+s[i+1:] for s in level for i in range(len(s)) if s[i] in '()'}

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According to DataEngPrep.tech, this is one of the most frequently asked Python/Coding interview questions, reported at 1 company. DataEngPrep.tech maintains a curated database of 1,863+ real data engineering interview questions across 7 categories, verified by industry professionals.

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