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- 精华
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- 积分
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- 经验
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- 魅力
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If there are 3 distinct symbols, we can arrange one or more of them on the
line without repetition:
1 symbol only: 3 possibilities.
2 symbols: 3*2= 6 possibilities.
3 symbols: 3*2=6 possibilites
Total possibilities = 15. 15 distint words reprented by 3 distinct symbols.
Bingo.
CCCC |
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