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Remove Invalid Parentheses

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Given a string s that contains parentheses and letters, remove the minimum number of invalid parentheses to make the input string valid.

Return a list of unique strings that are valid with the minimum number of removals. You may return the answer in any order.

class Solution(object):
    def removeInvalidParentheses(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        def dfs(s):
            mi = calc(s)
            if mi == 0:
                return [s]
            ans = []
            for x in range(len(s)):
                if s[x] in ('(', ')'):
                    ns = s[:x] + s[x+1:]
                    if ns not in visited and calc(ns) < mi:
                        visited.add(ns)
                        ans.extend(dfs(ns))
            return ans    
        def calc(s):
            a = b = 0
            for c in s:
                a += {'(' : 1, ')' : -1}.get(c, 0)
                b += a < 0
                a = max(a, 0)
            return a + b

        visited = set([s])    
        return dfs(s)

There are many different approaches to this problem but backtracking feels the most natural in my opinion.

Posted by Jamie Meyer 7 months ago

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