Google Kickstart 2019 Round G Book Reading
The most challenge part of this problem is that Q and N is a very larger number. So making a nested for loop will cause $N^2$ complexity. Instead, we use an array of size of MAX N to cache the answer. Thanks to multiple readers could probably have the same $R_i$. Another trick is that $R_i$ is not necessarily smaller than N, we should take into account and skip unnecessary operation. It is faster if we count the reading pages by stepping $R_i$ towards the N. A mistake I had was that I didn´t realize the answer size, the sum of Q readers’ reading pages will probably be larger the 32 bits, we must define the answer with at least 64 bits integer.