摘要： 题意 "题目链接" Sol 直接把$q_i$除掉 那么$E_j = \sum_{i = 1}^{j 1} q_i \frac{1}{(i j)^2} \sum_{i = j + 1}^n q_i \frac{1}{(i j)^2}$ 设$f_i = q_i, g_i = \frac{1}{i^2}$ 阅读全文