Check If Word Is Valid After Substitutions — LeetCode 1003 Python Solution

The problem

Given a string s, determine if it is valid. A string s is valid if, starting with an empty string t = "", you can transform t into s after performing the following operation any number of times: Insert string "abc" into any position in t.

Example

Input

s = "aabcbc"

Output

true

Explanation

"" -> "abc" -> "aabcbc"

Python solution

class Solution:
    def isValid(self, s: str) -> bool:
        if len(s) % 3:
            return False
        t = []
        for c in s:
            t.append(c)
            if ''.join(t[-3:]) == 'abc':
                t[-3:] = []
        return not t

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 1003. Check If Word Is Valid After Substitutions is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Stack.

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

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