Valid Parenthesis String

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Problem

Given a string containing '(', ')', and '*' — where '*' can be treated as '(', ')', or an empty string — determine whether the string can be interpreted as a valid parentheses sequence.

Examples

Example 1

Input:s = "(*))"

Output:true

Example 2

Input:s = "(()"

Output:false

Constraints

1 <= s.length <= 100

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How to approach it: the Greedy pattern

Make the choice that looks best right now, without reconsidering it later, and trust that a sequence of locally optimal choices adds up to a globally optimal answer. It only works when the problem actually has that property.

Look for this pattern when

Sorting the input by some key, then making one pass with simple local decisions, intuitively seems to produce the best answer.
The problem involves intervals, scheduling, or resource allocation where "always take the best available option" tends to work.

Read the full Greedy guide →

Video walkthroughs

Original problem on LeetCode ↗