四个ABC加一起有多少种组合方式
四个ABC，也就是AAAABBBBCCCC，一共可以有多少种组合？
A可以选0到4个，也就是可以有5种选择，B和C也是一样。一共有 5³ = 125个组合；
其中，全部不选（即空选）有1种，要剔除；
所以，一共有 125-1 = 124 种不同的组合。
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可以编程列出所有这些组合，当然手工也可以。
具体如下：
C，CC，CCC，CCCC，B，BC，BCC，BCCC，BCCCC，BB，BBC，BBCC，BBCCC，BBCCCC，BBB，BBBC，BBBCC，BBBCCC，BBBCCCC，BBBB，BBBBC，BBBBCC，BBBBCCC，BBBBCCCC，A，AC，ACC，ACCC，ACCCC，AB，ABC，ABCC，ABCCC，ABCCCC，ABB，ABBC，ABBCC，ABBCCC，ABBCCCC，ABBB，ABBBC，ABBBCC，ABBBCCC，ABBBCCCC，ABBBB，ABBBBC，ABBBBCC，ABBBBCCC，ABBBBCCCC，AA，AAC，AACC，AACCC，AACCCC，AAB，AABC，AABCC，AABCCC，AABCCCC，AABB，AABBC，AABBCC，AABBCCC，AABBCCCC，AABBB，AABBBC，AABBBCC，AABBBCCC，AABBBCCCC，AABBBB，AABBBBC，AABBBBCC，AABBBBCCC，AABBBBCCCC，AAA，AAAC，AAACC，AAACCC，AAACCCC，AAAB，AAABC，AAABCC，AAABCCC，AAABCCCC，AAABB，AAABBC，AAABBCC，AAABBCCC，AAABBCCCC，AAABBB，AAABBBC，AAABBBCC，AAABBBCCC，AAABBBCCCC，AAABBBB，AAABBBBC，AAABBBBCC，AAABBBBCCC，AAABBBBCCCC，AAAA，AAAAC，AAAACC，AAAACCC，AAAACCCC，AAAAB，AAAABC，AAAABCC，AAAABCCC，AAAABCCCC，AAAABB，AAAABBC，AAAABBCC，AAAABBCCC，AAAABBCCCC，AAAABBB，AAAABBBC，AAAABBBCC，AAAABBBCCC，AAAABBBCCCC，AAAABBBB，AAAABBBBC，AAAABBBBCC，AAAABBBBCCC，AAAABBBBCCCC，
total = 124
附：fortran代码
