### maroonrk's blog

By maroonrk, history, 22 months ago, We will hold AtCoder Grand Contest 053. This contest counts for GP30 scores.

The point values will be 400-700-900-1000-1400-2400.

We are looking forward to your participation! Comments (15)
 » Is It Rated?
•  » » Yes!
•  » » » 22 months ago, # ^ | ← Rev. 2 →   Correction: yes, for the range $[1200, \infty)$.
•  » » I also didn't manage to get the formula during the contest, but that's how I understand it. Let $X_i$ be the event where there is a greater value than $A_i$ among $B_1, \dots, B_{i+d}$. The probability we are looking for is $P(X_1 \cap \dots \cap X_n)$, which is equivalent to $P(X_1) \cdot P(X_2 | X_1) \cdot \dots \cdot P(X_n | (X_1 \cap \dots \cap X_{n-1}))$. Now it's easy to see that the mysterious $\frac{2i+d-1}{2i+d}$ is just $P(X_i | (X_1 \cap \dots \cap X_{i-1}))$ because $X_i$ won't hold only if $A_i$ is the greatest value among $A_1, \dots, A_i, B_1, \dots, B_{i+d}$.
 » For problem D, I don't understand the proof in the editorial that $t_{i,j}>=T_j$ for $i  » Is there any detailed proof for problem D "don't need to check$i