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证明过程

Posted by yizer at 2009-01-04 09:00:13 on Problem 3117
In Reply To:比赛场数乘3减去分数之和~~~没想过竟然这样~~~ Posted by:200630740629 at 2007-03-13 14:45:34 
ai*3 + bi*1 + ci*0 = di
3*sigma(ai) + sigma(bi) = sigma(di)
sigma(bi) = sigma(di) - 3*sigma(ai)
sigma(ai) + sigma(ci) + sigma(bi) = 2N
sigma(ai) = sigma(ci)
sigma(bi) = 2N - 2*sigma(ai)
sigma(ai) = sigma(di) - 2N

sigma(bi)/2 = 3*N - sigma(di)
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