补充: $sum4 = \sum_{i=l}^ri^2$ $ans=(r-l+1-r*l)*∑v[i]+(r+l)*∑v[i]*i-∑v[i]*i^2 $ by sdgzy @ 2018-10-04 10:35:57
抱歉,可以删掉这个贴子么,捂脸,ans忘记合并了.. by sdgzy @ 2018-10-04 10:36:43