12-6

A. APPLE buSinEss

[Hall定理] [树形DP]

C. 毛皮立方体

[ex_gcd] [二分图] [补图bfs]

12-7

C. 鱼和熊掌不可兼得

[交互] [构造] [思维] [分治]

12-8

A. 鱼死网破

[计算几何] [二分] [思维]

C. 浑水摸鱼

[Hash] [主席树] [数据结构]

12-9

A. 矩阵

[线性基] [贪心]

12-11

A. 不知道

[树链剖分] [李超线段树] [分块] [凸包] [数据结构]

12-13

A. GCD和LCM

[整除分块] [树状数组]

B. 平面图

[对偶图] [平面图] [并查集] [启发式分裂]