Minimum Additions to Make Valid String — LeetCode 2645 Python Solution

The problem

Given a string word to which you can insert letters "a", "b" or "c" anywhere and any number of times, return the minimum number of letters that must be inserted so that word becomes valid. A string is called valid if it can be formed by concatenating the string "abc" several times.

Example

Input

word = "b"

Output

2

Explanation

Insert the letter "a" right before "b", and the letter "c" right next to "b" to obtain the valid string "abc".

Python solution

class Solution:
    def addMinimum(self, word: str) -> int:
        s = 'abc'
        ans, n = 0, len(word)
        i = j = 0
        while j < n:
            if word[j] != s[i]:
                ans += 1
            else:
                j += 1
            i = (i + 1) % 3
        if word[-1] != 'c':
            ans += 1 if word[-1] == 'b' else 2
        return ans

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 2645. Minimum Additions to Make Valid 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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