Python C++速解Leetcode迴文1400 Construct K Palindrome Strings
關鍵：偶數長度的回文字串中所有字母都出現偶數，奇數長度的回文字串中除了一個例外其他所有字母都出現偶數。
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The key observation: palindrome strings of even lengths have all letters even occurrences, palindrome strings of odd lengths have all letters even occurrences but except one letter with odd occurrence.
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