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Maximum Difference Between Even And Odd Frequency I

Find the maximum difference between the frequencies of two characters whose counts have opposite parity.

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Problem Statement

Maximum Difference Between Even and Odd Frequency I

Given a string s, count how many times each character appears.

Your task is to find the largest possible value of:

frequency of one character−frequency of another character\text{frequency of one character} - \text{frequency of another character}

subject to the following condition:

  • the first character must have an even frequency,
  • the second character must have an odd frequency,
  • the two characters may be different.

If no valid pair of characters exists, return the closest safe answer for the problem variant, which is typically 0.

This is a frequency-analysis problem where you compare character counts and look for the best even-minus-odd difference.

Input Format

  • A string s consisting of lowercase English letters.
  • You may assume the string is non-empty unless the platform statement says otherwise.

Output Format

  • Return an integer: the maximum value of evenFrequency - oddFrequency over all valid character pairs.
  • If no valid pair exists, return 0.

Constraints

  • 1 <= s.length <= $10^{5}$ is a reasonable interview-style assumption for this variant.
  • Characters are typically lowercase English letters.
  • Time should be linear or near-linear in the length of the string.

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