Valid Parenthesis String — LeetCode 678 Python Solution

The problem

Given a string s containing only three types of characters: '(', ')' and '*', return true if s is valid. The following rules define a valid string: Any left parenthesis '(' must have a corresponding right parenthesis ')'.

Example

Input

s = "()"

Output

true

Python solution

class Solution:
    def checkValidString(self, s: str) -> bool:
        n = len(s)
        dp = [[False] * n for _ in range(n)]
        for i, c in enumerate(s):
            dp[i][i] = c == '*'
        for i in range(n - 2, -1, -1):
            for j in range(i + 1, n):
                dp[i][j] = (
                    s[i] in '(*' and s[j] in '*)' and (i + 1 == j or dp[i + 1][j - 1])
                )
                dp[i][j] = dp[i][j] or any(
                    dp[i][k] and dp[k + 1][j] for k in range(i, j)
                )
        return dp[0][-1]

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 678. Valid Parenthesis String is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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