Longest Palindrome LeetCode solution in Python

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class Solution:
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    def longestPalindrome(self, s: str) -> int:
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        letters = {}
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        for letter in s:  # count each letter and update letters dict
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            if letter in letters:
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                letters[letter] += 1
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            else:
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                letters[letter] = 1
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        plus1 = 0  # if there is a letter with count of odd ans must +=1
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        ans = 0
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        for n in letters.values():
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            if n == 1:  # 1 can only appear in the middle of our word
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                plus1 = 1
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            elif n % 2 == 0:
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                ans += n
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            else:
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                ans += n - 1
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                plus1 = 1
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        return ans + plus1