1453D - CheckpointsD - Checkpoints
D - Checkpoints1453D两个1之间肯定是独立的,卡在不会算期望(数学真的杀我设PnP_nPn为n个0的期望pn=12(Pn−1+1)+12(Pn−1+1+Pn)p_n = \frac{1}{2}(P_{n -1} + 1) + \frac{1}{2}(P_{n -1}+ 1+P_n)pn=21(Pn−1+1)+21(Pn−1+1+Pn)化简:Pn=Pn−1×2+2P_n = P_{n-1} \times 2 +2Pn=Pn−1×2+2#include &