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Grokking the Coding Interview Patterns

Solution: Remove Invalid Parentheses

Explore the backtracking method to remove the minimum number of invalid parentheses in a given string. Understand how to count unmatched parentheses and use recursive choices to build all valid expressions, ensuring balanced and unique results.

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Statement

You are given a string, s, that contains:

  • Lowercase English letters

  • Opening '(' and closing ')' parentheses

A string is considered valid if:

  1. All opening parentheses '(' are closed properly by a matching ')'.

  2. The parentheses are in the correct order and nesting.

  3. Letters can appear anywhere and do not affect validity.

Return all possible valid strings that can be formed by removing the minimum number of invalid parentheses. The answer must be a list of unique strings, in any order.

Constraints:

  • 1≤ ...