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转移自老blog

bzoj3527

链接

https://acm.taifua.com/bzoj/p/3527.html

题意

        那是一张图片

题解

        E_j=\sum_{i=0}^{j-1}{\frac{q_i}{(i-j)^2}}-\sum_{i=j+1}^{n}{\frac{q_i}{(i-j)^2}}\\
         if f[I]=\frac{1}{i*i}\\
        E_j=\sum_{I=0}^{j-1}{q_i*f(j-i)}-\sum_{I=j+1}^{n}{q_i*f(i-j)}\\
        前面一项下标和为定值，后面一项下标差为定值
        fft