# CC科技

$\sum\limits_{i=0}^\infty \dfrac{x^i}{i!}=e^x$ so inverse series for it is $e^{-x}=\sum\limits_{i=0}^\infty \dfrac{(-x)^i}{i!}$

https://discuss.codechef.com/questions/117004/binomsum-editorial

https://discuss.codechef.com/questions/91627/how-to-solve-seainvs

$A*B$ = $(x_{1}^2+x_{2}^2+x_{3}^2+x_{4}^2)*(y_{1}^2+y_{2}^2+y_{3}^2+y_{4}^2)$ =

$(x_{1}*y_{1}+x_{2}*y_{2}+x_{3}*y_{3}+x_{4}*y_{4})^2 +$

$(x_{1}*y_{2}-x_{2}*y_{1}+x_{3}*y_{4}-x_{4}*y_{3})^2 +$

$(x_{1}*y_{3}-x_{2}*y_{4}-x_{3}*y_{1}+x_{4}*y_{2})^2 +$

$(x_{1}*y_{4}-x_{4}*y_{1}+x_{2}*y_{3}-x_{2}*y_{3})^2$

https://discuss.codechef.com/questions/90269/foursq-editorial

Lindström–Gessel–Viennot lemma

det(（该矩阵的行列式）

https://discuss.codechef.com/questions/80665/chnbgmt-editorial

\begin{vmatrix}
f[1] & f[2] & \dots & f[k]\\
f[2] & f[3] & \dots & f[k+1] \\
\dots & \dots & \ddots & \dots \\
f[k] & f[k+1] & \dots & f[k+k-1]
\end{vmatrix}

https://discuss.codechef.com/questions/78427/dmcs-editorial

$(n+1) {\rm lcm} ({n \choose 0}, {n \choose 1}, \dots {n \choose k}) = {\rm lcm} (n+1,n,n-1, \dots n+1-k)$

http://discuss.codechef.com/problems/LOTERY

$B(x) = B_{0} + B_{1}x + B_{2}x^2 + ... B_{L-1}x^{L-1}$
$=A_{L-1} + A_{L-2}x + A_{L-3}x^2 + ... + A_{0}x^{L-1}$
$=x^{L-1} (A_{L-1}x^{-(L-1)} + A_{L-2}x^{-(L-2)} + ... + A_{0})$
$=x^{L-1} A(x^{-1})$
$=x^{L-1} A(1/x)$

https://discuss.codechef.com/questions/74772/mgch3d-editorial

https://discuss.codechef.com/questions/74081/distnum-editorial

https://discuss.codechef.com/questions/72678/nthcir-editorial

https://discuss.codechef.com/questions/71547/conpoin-editorial

https://discuss.codechef.com/questions/69002/sez-editorial

gcd(a, b, c, d..) = gcd(a, b-a, c-b, d-c...)支持区间加操作

https://discuss.codechef.com/questions/1588/dgcd-editorial

treap中求两节点间距离

https://discuss.codechef.com/questions/38704/cot5-editorial

Hall system及其转移

https://discuss.codechef.com/questions/1131/match-editorial

sin(mX)=2cos(X)sin((m − 1))−sin((m − 2)X)，所以有sin(k*X)的二阶线性递推