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#4 Four Letters
You are asked to create a text using only the letters A, B, C, and D. If all four-letter combinations (from AAAA to DDDD) are required to be included within the text, what should be the minimum length of this text ?
If the problem was asked for the letters A, and B, then the answer would be 5. Sample text: AABBA
你被要求只用字母A,B,C,D创建一个文本。如果所有的四字母组合(从AAAA到DDDD)必须包含在文本中,最小的文本长度是多少?
如果问题问的是字母A,B, 那么答案为5, 例子:AABBA
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